UC-NRLF 


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V  f 


GIFT   OF 
Harry  East  Miller 


AN 


ELEMENTARY 


MANUAL  OF  CHEMISTRY, 


ABRIDGED  FROM 

ELIOT  AND   STOKER'S  MANUAL, 

WITH   THE   CO-OPERATION   OF   THE   AUTHORS, 


BY 


WM.   RIPLEY  NICHOLS, 

PROFESSOR  OF   GENERAL   CHEMISTRY    IN  THE   MASSACHUSETTS 
INSTITUTE   OF  TECHNOLOGY. 


REVISED  EDITION. 


NEW   YORK: 
IVISON,   BLAKEMAN,  TAYLOR    AND   COMPANY, 


Entered,  according  to  Act  of  Congress,  in  the  year  1872,  by 

C.  W.  ELIOT.  F.  H.  STOKER  ANL-  W.  Jl.  NICHOLS, 
In  the  Office  of  the  Librarian  of  Congress,  at  Washington. 


Copyright,  18*7,  ty'C.  W.   firmer    F.  H    STUPED  &  W.  R.  NICHOLS. 


Copyright,  1880,  by  C.  W.  ELIOT,  F.  H.  STOKER  &  W.  R.  NICHOLS. 


EXTEACT  FROM  THE  PREFACE  TO  ELIOT  AND  STORER'S 
MANUAL  OF  INORGANIC  CHEMISTRY, 


"  IN  preparing  this  manual,  it  has  been  the  authors'  object 
to  facilitate  the  teaching  of  chemistry  by  the  experimental 
and  inductive  method.  .  .  .  The  authors  believe  that  the 
study  of  a  science  of  observation  ought  to  develop  and  disci- 
pline the  observing  faculties,  and  that  such  a  study  fails  of  its 
true  end  if  it  becom*  a  mere  exercise  of  the  memory. 

"The  minute  instructions,  given  in  the  descriptions  of  ex- 
periments and  printed  in  the  smaller  type,  are  intended  to 
enable  the  student  to  see,  smell  and  touch  for  himself;  these 
detailed  descriptions  are  meant  for  laboratory  use.  In  order 
to  mark  as  clearly  as  possible  the  distinction  between  chemistry 
and  chemical  manipulation,  the  necessary  instructions  on  the 
latter  subject  have  been  put  in  an  Appendix.  In  cases  in 
which  it  is  impossible  for  every  student  to  experiment  for  him- 
self, the  authors  hope  that  this  manual  will  make  it  easy  for 
the  teacher,  even  if  he  be  not  a  professional  chemist,  to  ex- 
hibit to  his  class,  in  a  familiar  and  inexpensive  manner, 
experiments  enough  to  supply  ocular  demonstration  of  the 
leading  facts  and  generalizations  of  the  science.  .  .  . 

"  There  is  little  original  in  the  book  except  its  arrangement 
and  method,  in  part,  and  its  general  tone.  The  authors  have, 
of  course,  drawn  largely  from  the  invaluable  compilations  made 
by  Gmelin,  Otto  and  Watts,  and  they  have  also  availed  them- 
selves freely  of  the  text-books  of  Stoeckhardt  and  Miller,  and  the 
writings  of  Hofmann." 


M81802 


PREFACE  TO  THE  ABRIDGMENT. 


THIS  Abridgment,  which  is  not  simply  an  abridgment,  is  a 
shorter  and  easier,  yet  a  more  comprehensive  manual  than  the 
original  one.  The  larger  manual  covers  only  inorganic  chem- 
istry ;  the  Abridgment  includes  the  elements  of  what  is  gen- 
erally called  organic  chemistry.  The  chapter  on  Carbon  in 
the  original  manual  has  been  subdivided  and  expanded,  so  as 
to  comprehend  the  principal  facts  and  theories  of  that  part  of 
chemistry  which  in  most  text-books  is  treated  as  a  distinct 
branch  under  the  name  of  organic  chemistry.  In  this  way 
the  compounds  of  carbon  are  studied  in  their  natural  place 
and  order,  and  the  student  has  a  fairer  view  of  the  whole 
science  than  he  is  likely  to  get  when  the  great  majority  of  the 
carbon  compounds  are  studied  quite  apart  from  carbon  itself  and 
from  some  of  its  longest-known  compounds,  and  after  all  the 
other  elements. 

In  preparing  the  new  chapters  on  the  compounds  of  carbon, 
the  authors  have  made  free  use  of  the  works  mentioned  above, 
especially  of  the  text-books  of  Stoeckhardt  and  Miller ;  they 
would  also  acknowledge  indebtedness  to  Prof.  Johnson's  "  How 
Crops  Grow,"  from  which  several  of  the  experiments  have  been 
taken.  These  experiments,  as  well  as  the  others  in  these  chap- 
ters, are  such  as  have  been  found  to  stand  the  test  of  actual 
performance  by  students. 


vi  PREFACE  TO  THE  ABRIDGMENT. 

This  manual  is  written  in  the  interest  of  no  particular  theory  ; 
the  typical  formulae  have  been  employed  in  many  cases  in  the 
chapters  on  carbon,  as  affording  a  convenient  method  of  repre- 
senting the  reactions  in  which  the  compounds  take  part.  Teach- 
ers who  desire  to  illustrate  more  fully  the  theory  of  the  subject 
may  refer  to  Cooke's  Chemical  Philosophy,  from  which  some  use- 
ful hints  have  been  taken  in  preparing  this  Abridgment. 

Teachers  who  put  the  Abridgment  into  the  hands  of  their 
pupils  will  find  it  useful  to  consult  the  larger  manual  for  addi- 
tional facts  and  experiments  and  fuller  explanations. 

MARCH,  1872. 


PREFACE  TO   THE   SECOND   REVISED   EDITION. 


FEOM  time  to  time  since  the  first  issue  of  the  book,  corrections 
have  been  made  of  such  errors  as  have  come  to  the  notice  of  the 
authors.  The  present  edition  has  been  thoroughly  revised.  The 
most  important  changes  in  the  first  revised  edition  were  in  Chap- 
ters IX  and  XI,  and  in  §§  27,  28,  36,  63,  and  76  ;  some  new 
matter  was  also  added.  In  the  present  edition,  besides  minor 
corrections  and  additions,  Chapter  VI  has  been  rewritten.  The 
page  numbers,  however,  as  a  rule,  have  not  been  altered,  so  that 
where  the  book  is  already  in  use  there  will  be  no  difficulty  in 
the  way  of  the  gradual  introduction  of  this  new  edition. 

JUNE,  1880. 


TABLE  OF  CONTENTS. 


PA9IS 

Introduction.  —  Subject  matter  of  chemistry.  Chemical  and  physical 
changes.  Analysis  and  synthesis.  Elements.  Fact  and  theory  ....  1-4 

Chap.  I. —  Air.  Atmospheric  pressure.  Analysis  of  air.  Oxygen  and  nitro- 
gen   4-8 

Chap.  II.  —  Oxygen.  Preparation  and  properties  of  oxygen.  Oxygen 
supports  combustion.  Oxides.  Wide  diffusion  of  oxygen.  Oxidation  .  .  .  9-11 

Chap.  III.  —  Nitrogen.     Preparation  and  properties  of  nitrogen       .        .      11-13 

Chap.  IV.  —  Water.  Properties  of  water.  The  gramme.  Specific  gravity. 
Ice.  Steam.  Analysis,  electrolysis  and  synthesis  of  water.  Atoms  and  mole- 
cules. Atomic  weights.  Distillation.  Solution 13-22 

Chap.  V.  —  Hydrogen.  Preparation  of  hydrogen.  Properties  of  hydro- 
gen. Lightness,  diffusive  power,  inflammability  of  hydrogen.  Hydrogen  does  not 
support  combustion.  Oxy -hydrogen  blowpipe.  Combustibles  and  supporters  of 
combustion 23-30 

Chap.  VI. — Compounds  of  nitrogen  with  oxygen  and  hydro- 
gen. Nitrous  oxide.  Its  composition  and  properties.  Nitric  oxide.  Its 
preparation,  properties,  and  composition.  Nitrogen  peroxide.  Liquefaction  of 
gases.  Nitric  anhydride.  Nitrous  anhydride.  Chemical  compounds  and  me- 
chanical mixtures.  Law  of  multiple  proportions.  Air  a  mixture.  Nitric  acid. 
Acid  and  alkaline  reaction.  Acids,  bases  and  salts.  Ammonia.  Composition, 
source  and  preparation  of  ammonia.  Preparation  of  ammonia  water  .  .  30-49 

Chap.  VII.  —  Chlorhydric  acid.  Properties,  composition  and  prep- 
aration of  chlorhydric  acid.  Chlorides.  Quantivalence.  Aqua  regia.  Practical 
application  of  chemical  equations 49-56 

Chap.  VIII.  —  Chlorine.  Preparation  and  properties  of  chlorine.  Chlo- 
rine unites  readily  with  hydrogen.  Certain  metals  burn  in  chlorine.  Chlo- 
rine both  combustible  and  a  supporter  of  combustion  with  reference  to 
hydrogen.  Chlorine  as  a  bleaching  agent  and  disinfectant.  Oxygen  com- 


viii  CONTENTS. 

pounds  of  chlorine.  Bleaching-powder  —  Bromine.  Occurrence  and  proper- 
ties of  bromine.  Bromhydric  and  bromic  acids.  —  Iodine.  Source  and  prop- 
erties of  iodine.  lodohydric  and  iodic  acids.  Nitrogen  iodide.  The  chlorine 
group.  —  Fluorine.  Occurrence  of  fluorine  Fluorhydric  acid.  Etching 
glass  .  •  55-67 

Chap.  IX.— Ozone.  An  allotropic  form  of  oxygen.  Preparation  of 
ozone.  Ozone  an  oxidizing,  bleaching,  and  disinfecting  agent  Antozone  clouds  .  68-71 

Chap.  X.  --  Sulphur,  selenium  and  tellurium.  Source  of  sul- 
phur. Action  of  sulphur  when  heated.  Soft  sulphur  Crystallization  of  sulphur. 
Systems  of  crystallization.  Sulphur  unites  with  other  elements.  Prepa- 
ration, composition  and  properties  of  hydrogen  sulphide.  Sulphurous  an- 
hydride. Preparation  and  properties.  Sulphurous  acid  bleaches.  Sulphuric 
acid.  Oxidizing  and  reducing  agents.  Manufacture  of  sulphuric  acid.  Prop- 
erties of  sulphuric  acid.  Sulphates.  Fuming  sulphuric  acid.  Occurrence 
of  selenium  and  tellurium.  Sulphur,  selenium  and  tellurium  allied  to 
oxygen ...  71-86 

Chap.  XT.  —  Combination  by  volume.  Product  Tolume.  Relation 
of  combining  weight  to  specific  gravity.  Molecular  condition  of  the  elementary 
gases  -  ' 87-92 

Chap.  XII.  —  Phosphorus.  Properties  of  phosphorus.  Allotropic  modi- 
fications of  phosphorus.  Compounds  of  phosphorus  and  hydrogen.  Phosphorus 
and  oxygen.  Phosphoric  anhydride.  Phosphoric  acid.  Empirical  and  rational 
formulae.  Typical  formulae 92-102 

Chap.  XIII.  —  Arsenic,  antimony  and  bismuth.  Properties  of 
arsenic.  Hydrogen  arsenide.  Arsenious  anhydride  Poisonous  character  and  uses 
of  arsenious  anhydride.  Other  compounds  of  arsenic.  —  Antimony  occurs  native. 
Properties  and  uses  of  antimony.  Compounds  of  antimony  with  hydrogen, 
oxygen  and  with  chlorine.  —  Properties  of  bismuth.  The  nitrogen  group  of 
elements 102-108 

Chap.  XIV.  —  Carbon.  Wide  distribution  and  importance  of  carbon  and 
its  compounds.  Allotropic  modifications  of  carbon.  Diamond.  Graphite. 
Gas-carbon.  Coke.  Anthracite  and  bituminous  coal  Charcoal.  Lamp- 
black. Charcoal  a  reducing  agent.  Charcoal  absorbs  gases.  Charcoal  a 
disinfecting  agent.  Charcoal  decolorizes.  Carbonic  acid  and  carbonates. 
Preparation  and  properties  of  carbonic  acid.  Solubility  of  carbonic  acid. 
Carbonic  acid  produced  in  the  processes  of  decay,  fermentation  and  respi- 
ration. Carbon  protoxide.  Properties.  "Carbon  protoxide  poisonous.  Re- 
ducing power  and  inflammability  of  carbon  protoxide.  Combustion.  Lumi- 
nosity of  flames.  All  flames  gas-flames.  Structure  of  flames.  Blowpipe  flames. 
Chimneys.  Kindling  temperature.  Carbon  and  sulphur.  Carbon  bisul- 
phide    109-135 

Chap.  XV.  —  Carbon  (continued).  Organic  chemistry.  Compounds  of 
carbon  and  nitrogen.  Cyanogen  and  cyanhydric  acid.  Hydrocarbons. 
Methyl  hydride  or  marsh-gas.  Preparation.  Chloroform.  Manufacture  of 
illuminating  gas.  Composition  of  the  gas.  Marsh-gas  series  Petroleum. 


CONTENTS. 


IX 


Alcohol.  Yeast.  Fermentation.  Fractional  distillation.  Fractional  conden- 
sation. The  alcohols.  Preparation  and  properties  of  ether.  The  ethers. 
Mercaptans.  Acetic  acid.  Preparation  of  vinegar.  Chloral.  Fatty  acid  series. 
Acetic  and  formic  acids.  Natural  fats  and  oils.  Manufacture  of  soap.  Prepara- 
tion of  glycerin.  Nitroglycerin.  Vegetable  oils.  Drying  oils.  Essential  oils. 
Oil  of  cloves.  Oil  of  turpentine.  Camphor 135-163 

Chap.  XVI.  —  Carbon  (continued).  Homologous  series  of  hydrocarbons. 
Olefiant  gas  or  ethylene.  Preparation  of  Dutch  liquid.  Olefiant-gas  series. 
Glycols.  Definition  of  the  term  alcohol.  Phenyl  series.  Distillation  of  coal- 
tar  Benzol,  nitro-benzol  and  aniline  Constitution  of  aniline.  Aniline  colors. 
Preparation  and  properties  of  phenic  or  carbolic  acid ;  of  picric  acid.  Naph- 
thalin  and  anthracene.  Products  of  the  destructive  distillation  of  wood. 
Oil  of  bitter  almonds.  Relation  of  the  oil  of  almonds  to  the  phenyl  series. 
Acetylene  series 163-173 

Chap.  XVII.  —  Carbon  (continued).  Organic  compounds  the  direct  pro- 
duct of  the  growth  of  animals  and  plants.  Sugar.  Manufacture  of  sugar. 
Properties  of  cane-sugar.  Dextrose  or  grape-sugar.  Levulose  or  fruit- 
sugar.  Lactose  or  milk-sugar.  Fermentation.  Fermented  and  distilled 
liquors.  Starch,  occurrence  and  properties  of.  Dextrin.  Gluten.  Bread. 
Properties  of  cellulose  or  woody  fibre.  Vegetable  parchment.  Gun-cotton. 
Gum.  Pectose.  Balsams.  Resins.  Character  and  solubility  of  the  resins. 
Gum-resins.  Caoutchouc  and  gutta-percha.  Fossil  resins.  Vegetable  acids. 
Preparation  and  properties  of  oxalic  acid.  Malic  acid.  Source,  preparation  and 
uses  of  tartaric  acid.  Citric  acid.  Varieties  and  properties  of  tannic  acid  Gallic 
acid.  Vegetable  alkaloids.  Opium.  Strychnine.  Organic  coloring  matters. 
Dyeing.  Illustration  of  methods  of  dyeing.  Indigo.  Indigo  dyeing.  Physio- 
logical chemistry.  Complexity  of  the  chemical  substances  concerned  in  the  vital 
functions.  Properties  of  albumin.  Fibrin.  Casein.  Milk,  butter  and  cheese. 
Gelatin  and  glue.  Decay  of  organic  substances.  Antiseptic  and  preservative 
agents  176-204 

Chap.  XVIII.  —  Silicon  and  boron.  Abundance  of  silicon.  Silicic  an 
hydride  or  silica.  Water-glass.  Silicates.  Various  sorts  of  glass.  Silica  is  attacked 
by  fluorhydric  acid.  Silicon  fluoride  and  fluosilicic  acid  Allotropic  modifications 
of  silicon.  Silicon  in  organic  compounds.  —  Occurrence  of  boron  in  nature. 
Boracic  acid  and  boracic  anhydride 204-208 

Chap.  XIX.  —  Sodium.  Abundance  of  the  element.  Common  salt  or  so- 
dium chloride.  Manufacture  of  salt.  Solubility  of  common  salt!  Sodium  sulphate. 
Glauber's  salt.  Manufacture  of  sodium  carbonate.  Reverberatory  furnace. 
"  Bicarbonate  of  soda.''  The  metal  sodium.  Sodium  decomposes  water.  Sodium 
hydrate  or  caustic  soda.  Soap.  Cleansing  action  of  soap.  Formation  of  salts. 
Borax.  Other  compounds  of  sodium  ...  - 209-219 

Chap.  XX.  —  Potassium.  Source  of  potassium  compounds.  Potash  and 
pearlash.  Potassium  carbonate.  Potassium  hydrate.  Uses  of  caustic  potash 
The  metal  potassium.  Potassium  decomposes  water.  Burns  in  carbonic  acid. 
Potassium  cyanide  a  reducing  agent.  Potassium  ferro-  and  ferri-cyanide.  Potas- 
sium nitrate  formed  in  nature.  Oxidizing  power  of  potassium  nitrate.  Gun- 
powder. Potassium  chlorate.  Potassium  tartrate  .  .  .  .  .  .  219-228 


x  CONTENTS. 

Chap.  XXI.  —  Ammonium  salts.  The  group  of  atoms,  ammonium. 
Ammonia-water.  Ammonium  chloride.  Ammonium  sulphate.  Ammonium  ni- 
trate. Ammonium  carbonates  and  sulphides.  Isomorphism  ....  228-231 

Chap.  XXII.  —  Lit hium,    rubidium,   caesium   and    thallium. 

Properties  of  lithium.      Spectrum  analysis.     Occurrence  and  properties  of  ru- 
bidium, caesium  and  thallium 231-234 

Chap.  XXIII.  —  Silver.  Ores  of  silver.  Properties  of  the  metal.  The 
term  metal.  Silver  nitrate.  Silver  chloride.  Other  silver  salts.  Photography.— 
The  alkali  group .  234-241 

Chap.  XXIV.  —  Calcium,  barium,  strontium  and  lead.  Calci- 
um. Calcium  carbonate.  Stalactites  and  stalagmites.  Calcium  oxide.  Calcium 
hydrate.  Air-slaked  lime.  Milk  of  lime.  Mortar.  Lime  as  a  base.  Calcium  sul- 
phate. Gypsum  and  plaster  of  Paris.  Hardness  of  water.  Phosphates  of  calcium. 
Calcium  chloride.  Calcium  hypochlorite.  Oxygen  from  bleaching-powder.— 
Strontium  and  barium  resemble  calcium.  Flame  colored  by  salts  of  strontium 
and  barium.— Ores  of  lead.  The  metal  lead.  Separation  of  lead  and  silver. 
Action  of  air  and  water  on  lead.  Oxides  of  lead.  Lead  sulphide.  Salts  of 
lead 241-250 

Chap.  XXV.— Magnesium,  zinc,  and  cadmium.  Various  nat- 
ural compounds  of  magnesium.  The  metal.  Oxide  of  magnesium.  Salts  of  mag- 
nesium.—  Ores  of  zinc.  Properties  of  metallic  zinc.  The  galvanic-current.  The 
lead-tree.  Electro-chemical  relations  of  the  elements.  The  terms  negative  and 
positive.  Salts  of  zinc.  —  Cadmium 251-257 

Chap.  XXVI.  —  Aluminum,  chromium,  manganese,  iron,  co. 
bait  and  nickel.  Abundance  of  aluminum.  Properties  of  the  metal.  Alu- 
mina. Aluminum  hydrate.  Lakes.  Mordants.  Aluminum  sulphate.  Alums. 
Aluminum  silicates.  Earthenware. — Glucinum — Indium. — Ores  of  chromium. 
Chromium  sesquioxide.  Chromium  sulphate  and  chrome  alum.  Chromic  anhy- 
dride and  chromic  acid.  —  Compounds  of  manganese.  Potassium  permanganate. — 
Ores  of  iron.  Extraction  of  iron  from  its  ores.  Cast-iron.  The  blast-furnace. 
Wrought-iron.  Puddling.  Steel.  The  Bessemer  process  Oxides  and  hydrates 
of  iron.  Ferrous  and  ferric  salts.  Ferrous  sulphate  or  copperas.  Method  of  re- 
ducing indigo.  Iron  silicate.  Ferro-  and  ferri -cyanides.  Prussian  blue.  Iron 
sulphides.  —  Cobalt  and  nickel.  —  The  sesquioxide  group.  —  Uranium  .  .  .  258-274 

Chap.  XXVII.  —  Copper  and  mercury.  Occurrence  of  copper  in  na- 
ture. Ores  of  copper.  Properties  of  copper.  Alloys  of  copper.  Oxides  of  copper. 
Copper  sulphate.  Copper  acetates.  —  Ores  of  mercury.  Properties  of  the  metal. 
Oxides  of  mercury.  Chlorides  of  mercury.  Amalgams.  Detection  of  mercury  .274-279 

Chap.  XXVIII.  —  Tin  Ores  of  tin.  Properties  of  the  metal.  Alloys  of 
tin.  Compounds  of  tin 279-281 

Chap.  XXIX.  —  Gold  and  Platinum.  Occurrence  of  gold  in  nature. 
Gold  a  noble  metal.  Alloys  of  gold.  Salts  of  gold.  —  Occurrence  of  platinum. 
Uses  of  platinum.  Platinum  black,  and  platinum  sponge.  Platinum  group  .  281-285 

Equivalent  weights.  Nomenclature.  Quantivalence.  Graphic  symbols.  Oxi- 
dation and  reduction.  Volumetric  interpretation  of  symbols.  Coincidence  of 
atomic  weight  and  unit-volume  weight.  Electrical  relations  of  the  atoms  .  .  288-294 


CONTENTS.  XJ 

Chap.  XXX.— Atomic  weights  and  classification  of  the  elements.  Alpha- 
betical list  of  the  elements.  Groups  of  the  elements 295-296 

Appendix.  Glass-tubing.  Cutting  and  cracking  glass.  Bending,  drawing 
and  closing  glass-tubes.  Blowing  bulbs.  Lamps.  The  Bunsen  burner.  Wire- 
gauze  lamps.  Blast-lamps.  Bellows.  Blowpipes.  Caoutchouc  tubing  and  stop- 
pers. CorKs  and  cork-cutters.  Iron-stand,  sand-bath  and  wire-gauze.  Triangles. 
Pneumatic  trough.  Gas-holders.  Deflagrating-spoon.  Platinum  foil  and  wire. 
Filtering  Folding  filters.  Drying  gases.  Water-bath.  Self-regulating  gas- 
gecerator.  Glass  retorts.  Flasks.  Beakers.  Test-tubes.  Test-glasses.  Pi- 
pettes. Measuring-glasses.  Porcelain  dishes  and  crucibles.  Rings'  to  support 
round-bottomed  vessels.  Crucibles.  Iron  retort.  Tongs.  Furnaces.  Mortars. 
Spatulae.  Thermometers.  The  metrical  system  of  weights  and  measures.  Table 
for  the  conversion  of  grammes  into  grains,  centimetres  into  inches  and  litres  into 
quarts.  Table  for  the  conversion  of  degrees  of  the  centigrade  scale  into  degrees  of 
Fahrenheit's  scale.  Order-list  of  chemicals  and  apparatus i-xly 


ELEMENTARY 
MANUAL  OF  CHEMISTRY, 


INTRODUCTION. 

1.  THE  various  objects  which  constitute  external  nature  pre- 
sent to  the  observing  eye  an  infinite  variety  of  quality  and 
circumstance.  Some  bodies  are  hard,  others  soft ;  some  are 
brittle,  others  tough  or  elastic.  Some  natural  objects  are  en- 
dowed with  life,  —  they  grow  ;  others  are  lifeless,  —  they  may 
be  moved,  but  do  not  move  themselves.  Some  bodies  are  in  a 
state  of  incessant  change ;  while  others  are  so  immovable  and 
unchangeable  that  they  seem  everlasting.  In  the  midst  of 
this  infinite  diversity  of  external  objects,  where  lies  the 
domain  of  Chemistry  ?  What  is  the  subject-matter  of  this 
science  ? 

When  air  moves  in  wind,  when  water  moves  in  tides  or  in 
the  fall  of  rain  or  snow,  the  air  and  water  remain  air  and 
water  still ;  their  constitution  is  not  changed  by  the  motion,' 
however  frequent  or  however  great.  A  bit  of  granite,  thrown 
off  from  the  ledge  by  frost,  is  still  a  bit  of  granite,  and  no  new 
or  altered  thing.  If  a  solid  piece  of  iron  be  reduced  to  filings, 
each  finest  morsel  is  metallic  iron  still,  of  the  same  substance 
as  the  original  piece,  as  will  appear  to  the  eye,  if  a  morsel  be 
sufficiently  magnified  under  the  microscope.  The  melted,  fluid 
lead  in  the  hot  crucible,  and  the  solid  lead  of  the  cold  bullet 
cast  from  it,  are  the  same  in  substance,  only  differing  in  respect 
1 


2  CHEMICAL  CHANGES.  [§  2. 

to  temperature.  In  all  these  cases,  the  changes  are  external 
and  ;.ica-essential,  not  intimate  and  constitutional  :  they  are 
called  physical  changes. 

2.  W.ben  iron  is  exposeo!  to  the  weather,  it  becomes  covered 
wHh  a  brownish,  earthy  coating,  which  bears  no  outward  resem- 
blance to  the  original  iron;  and,  if  exposed  long  enough,  the 
metal  completely  disappears,  being  wholly  changed  into  this 
very  different  substance,  rust.  A  piece  of  coal  burns  in  the 
grate  and  soon  vanishes,  leaving  nothing  but  a  little  ashes. 
Dead  vegetable  or  animal  matters,  buried  in  the  ground,  soon 
putrefy,  decay,  and  disappear.  So,  too,  the  fragment  of  granite 
which  frost  has  broken  from  the  ledge,  exposed  for  centuries 
to  the  action  of  air  and  rain,  becomes  changed ;  it  "  weathers," 
and  after  a  time  could  no  longer  be  recognized  as  granite.  All 
these  changes  involve  alterations  in  the  intimate  constitution 
of  the  bodies  which  undergo  them  :  they  are  called  chemical 
changes. 

Experiment  1.  —  Mix  thoroughly  3  grammes  (for  Tables  of  the 
Metrical  System  of  Weights  and  Measures,  see  Appendix)  of  coarsely- 
powdered  sulphur  with  8  grammes  of  copper-filings  or  fine  turnings. 
Fig.  l.  Put  the  mixture  into  a  tube  of  hard  glass,  No.  3, 

about  12-  centimetres  long,  and  closed  at  one 
end.  (For  the  manipulation  of  tubing,  see 
Appendix,  §§  1-4.)  Hold  the  tube  by  the  open 
end  with  the  wooden  nippers,  as  in  Fig.  1,  and 
heat  the  mixture  over  the  gas-lamp  (Appendix, 
§  5),  until  it  suddenly  glows  vividly  at  the  in- 
stant when  the  copper  and  sulphur  combine. 

Before  heat  was  applied,  the  mixture  of  the 
two  substances  was  simply  mechanical,  and  the 
copper  might  have  been  completely  separated 
from  the  sulphur,  by  due  care  and  patience  ;  but, 
during  the  ignition,  the  copper  and  sulphur  have  united  chemically, 
and  there  has  been  formed  a  substance,  which,  while  containing  both, 
has  no  external  resemblance  to  either.  In  the  new  body  the  eye  can 
detect  neither  copper  nor  sulphur. 

Processes  by  which  the  whole  character  and  appearance   of 


§3.] 


ANALYSIS  AND  SYNTHESIS. 


the  bodies  concerned  are  changed,  as  in  this  experiment,  so  that 
essentially  new  bodies  are  formed  from  the  old,  are  chemical 
processes.  It  is  the  function  of  the  chemist,  on  the  one  hand, 
to  investigate  the  action  of  each  substance  on  every  other,  and 
to  study  the  properties  of  the  combinations  resulting  from  this 
action  ;  and,  on  the  other,  to  separate  compound  bodies  into 
their  simpler  constituents  :  he  further  seeks  the  general  laws 
by  which  the  intimate  combinations  of  matter  are  controlled. 
With  these  ends  in  view,  he  endeavors  to  pull  to  pieces,  or,  in 
technical  language,  to  analyze,  every  natural  substance  on  which 
he  lays  hands.  Having  thus  found  out  the  composition  of  the 
substance,  he  seeks  to  put  it  together  again,  or  to  recompose  it 
out  of  its  constituent  parts.  By  one  or  both  of  these  two  pro- 
cesses, —  analysis  (unloosing)  and  synthesis  (putting  together), 
—  the  chemist  studies  all  substances. 

3.  The  first  question  which  the  chemist  asks  himself  con- 
cerning every  natural  substance  is,  Of  ivhat  is  it  composed  ? 
He  then  attempts  to  resolve  the  substance  into  simpler  consti- 
tuents. If  he  succeeds  in  decomposing  it,  he  obtains  the  answer 
to  this  first  question  ;  if  the  body  can  not  be  decomposed  by  any 
known  method  of  analysis,  the  substance  must  be  regarded  as 
being  already  at  its  simplest.  Such  simple  bodies  are  called 
elements,  Secondly,  the  chemist  asks,  How  does  this  new  sub- 
stance comport  itself  when  brought  into  contact  with  other 
substances  already  familiar  ?  There  are  sixty-four  substances 
which  are,  at  present,  admitted  to  be  simple,  primary  substances, 
or  elements  ;  other  elementary  substances  may  hereafter  be  dis- 
covered, and  substances  which  are  now  regarded  as  elements 
may  hereafter  be  found  to  be  compound  ;  so  that  the  number  of 
the  substances  considered  as  elements  is  subject  to  change.  Of 
compound  bodies,  formed  by  the  union  of  these  elements  with 
each  other,  we  find  a  series,  numbering  many  thousands,  in  the 
inorganic  kingdom  of  nature,  comprising  all  the  diversified 
mineral  constituents  of  the  earth's  crust ;  while  another  series, 
far  more  complex  in  composition,  and  almost  innumerable  in 
multitude,  exists  in  the  vegetable  and  animal  world.  The  task 
of  the  chemist  in  thoroughly  answering  his  second  question 


£  FACT  AND   THEORY.  f§  4. 

would  clearly  be  endless,  were  it  not  for  the  existence  of  general 
properties  common  to  extensive  groups  of  both  elementary  and 
compound  bodies,  and  of  general  laws  which  chemical  processes 
invariably  obey. 

While,  therefore,  the  chemist  seeks  the  answers  to  the  two 
fundamental  questions  above  stated,  he  is  at  the  same  time  in- 
quiring what  relations  exist  between  the  properties  of  a  body 
and  its  composition ;  and  he  is  also  studying  that  natural  and 
invariable  sequence  of  chemical  phenomena,  which,  when  fully 
known,  will  constitute  the  perfect  science  of  chemistry.  , 

4.  Generalizations  from  observed  facts,  so  long  as  they  are 
uncertain  and  incomplete,  are  called  hypotheses  and  theories  ; 
when  tolerably  complete  and  reasonably  certain,  they  are  called 
laws.  The  attention  of  the  student  should  be  constantly  di- 
rected to  the  keen  discrimination  between  facts  and  the  spec- 
ulations founded  upon  those  facts  ;  between  the  actual  evidence 
of  our  trained  senses  brought  intelligently  to  bear  upon  chemical 
phenomena,  and  the  reasonings  and  abstract  conclusions  based 
upon  this  evidence  ;  between,  in  short,  that  which  we  may  know 
and  that  which  we  may  believe. 


CHAPTER   I. 

AIR. 

5.  We  are  everywhere  surrounded  by  an  atmosphere  of  in- 
risible  gas,  called  air.  In  motion,  it  is  wind,  and  we  recognize 
its  existence  by  its  powerful  effects  ;  but  in  the  stillest  places  it 
exists  as  well.  The  presence  of  air  in  any  bottle,  flask  or  other 
hollow  vessel  which  is  empty,  in  the  sense  in  which  this  word  is 
ordinarily  applied,  can  be  shown  very  simply  by  attempting  to 
put  some  other  substance  into  the  vessel,  under  such  conditions 
that  the  air  can  not  pass  out  from  it. 

If,  for  example,  we  wrap  around  the  throat  of  a  funnel  with  narrow 
outlet,  a  strip  of  moistened  cloth  or  paper,  so  that  the  funnel  shall  fit 


g  7.]  ATMOSPHERIC  PRESSURE.  5 

tightly  into  the  neck  of  a  bottle,  and  then  fill  the  funnel  with  water, 
we  shall  observe  that  this  water  does  not  run  into  the  bottle.  The 
bottle  which  we  have  called  empty  is  in  reality  filled  with  air,  and 
it  is  this  air  which  prevents  the  water  from  entering  the  bottle.  If, 
now,  the  funnel  be  lifted  slightly,  so  that  the  mouth  of  the  bottle 
shall  no  longer  be  completely  closed  by  it,  the  air  within  the  bottle 
will  pass  out,  and  the  water  in  the  funnel  will  instantly  flow  down. 

6.  We  may  actually  pump  the  air  out  of  the  bottle  by  means 
of  an  apparatus  known  as  the  air-pump  ;  or  we  may  remove  a 
portion  of  the  air  by  suction. 

Exp.  2.  —  Fit  to  any  small  flask  or  bottle  a  perforated  cork  (for 
the  manipulation  of  corks,  see  Appendix,  §  9),  to  which  has  been 
adapted  a  short  piece  of  glass  tubing,  No.  7.  Slip  over  the  end  of 
this  glass  tube  a  short  piece  of  caoutchouc  tubing.  Suck  part  of  the 
air  out  of  the  flask,  and  then  nip  the  caoutchouc  tube  with  thumb 
and  finger,  so  that  no  air  shall  re-enter.  Immerse  the  neck  of  the 
flask  in  a  basin  of  water,  and  release  the  caoutchouc  tube.  Water 
will  instantly  rise  into  the  flask  to  take  the  place  of  the  air  which  has 
been  sucked  out. 

7.  The  water,   in  this  experiment,  is  forced  into  the  flask 
by  the  pressure  of  the  superincumbent  atmosphere.     Air  has 
weight,  a  litre  of  dry  air,  at  the  temperature  of  0°,  weighing 
1.2932  gramme.     It  has  been  determined  that  the  force  with 
which  the  air  is  attracted  to  the  earth  is  on  an  average  equal 
to  a  weight  of  1.033  kilogramme  to  the  square  centimetre  of 
surface.     That  is  to  say,  the  ocean  of  air  above  us  presses  down 
upon  every  square  centimetre  of  the  earth's  surface  with  a  force 
equal  to  that  which  would  be  exerted  by  a  bar  of  metal,  or  other 
substance,  a  centimetre  square  in  section  and  long  enough  to 
weigh  1.033  kilogramme.     If  such  a  bar  were  constructed  of 
iron,  it  would  be  1.3  metre  long  ;  if  of  water,  —  and  a  bar  of 
this  substance  can  readily  be  made  by  enclosing  the  water  in  a 
tube,  —  it  would  be  10.33  metres  long. 

In  addition  to  the  qualities  already  mentioned,  we  find  air  to 
be  tasteless  and  odorless ;  it  is  also  colorless  when  in  small 
depths,  but  exhibits  a  blue  tint  when  seen  in  large  masses,  as 
when  in  the  absence  of  clouds  we  look  at  the  sky  or  at  a  distant 
mountain, 


6  ANALYSIS  OF  AIR.  [§  8.. 

8.  We  will  now  proceed  to  study  the  chemical  properties  of 
air,  first  asking  the  question,   Of  what  is  air  composed  ?     When 
a  bar  of  iron  is  heated  in  the  air,  as  at  a  blacksmith's  forge,  it, 
becomes  covered  with  a  coating,  which  flies  off  in  scales  when 
the  iron  is  beaten  upon  the  anvil.     If  a  piece  of  wire  or  ribbon 
made  of  the  metal  magnesium  be  touched  with  a  match,  it  will 
take  fire  and  burn,  and  be  entirely  converted  into  white  ashes. 
With  the  exception  of  gold,  silver,  platinum  and  a  few  other 
exceedingly  rare   metals,   all   the   metals  burn,   or   rust,   when 
heated  in  the  air.     If  no  air  be  present,  this  rust  or  ashes  will 
not  be  formed,  however  long  or  intensely  the  metal  may  be 
heated.     But  in  what  manner  is  the  rust  formed  1     Is  something 
driven  out  of  the  metal  into  the  air,  or  does  something  come 
out  of  the  air  and  unite  with  the  metal  1     This  question  may  be 
answered   by  experiment.     If  a   weighed   quantity  of   tin-foil 
be  heated  in  a  porcelain  dish  over  the  gas-lamp,  the  metal  is 
gradually  converted  into-  white  ashes.     When  all  the  metal  has 
thus  been  changed,  and  the  ashes  have  been  allowed  to  cool,  it 
will  be  found  that  the  ashes  are  very  sensibly  heavier  than  the 
original  metal. 

9.  It   is   possible  that  during  the  heating   the   metal   may 
have  lost  something,  but  it  is  certain  that  it  has  gained  more. 
We  have,   therefore,   taken  something  out  of  the   air,   which, 
gaseous  in  the  air,  has  become  solid  in  the  white  ashes  of  the 
tin.     It  would  be  possible  to  recover  from  the  tin-rust  the  some- 
thing thus  taken  from  the  atmosphere,  and  to  compare  it  with 
common  air,  and  so  learn  whether  the  matter  which  combined 
with  the  heated  tin  is  air  itself,  or  only  a  part  of  the  air.     The 
process,  however,  would  be  a  circuitous  one.     From  the  rust 
of  other  common  metals,  as  from  that  of  mercury,  for  example, 
the   absorbed   gas   can   be   very   easily  expelled.      If   metallic 
mercury  be  heated  for  a  long  time  in  the  air,  it  will  be  en- 
tirely converted  into  a  red  substance  known  as  "  red  oxide  of 
mercury." 

Exp.  3.  —  Put  into  a  tube  of  hard  glass,  No.  2,  about  12  c.  m.  long, 
10  grammes  of  the  red  mercury  oxide.     Tubes  of  hard  glass,  for  such 


J  9.]  ANALYSIS  OF  AIR.  7 

purposes,  will  be  hereafter  designated  as  "  ignition-tubes."    Attach  to 
this  ignition-tube,  by  means  of  a  perforated  cork  or  caoutchouc  stop- 
per, a  delivery-tube  of  glass,  No.  8,  Fig.  2. 
of  such  shape  and  length  that  it 
shall    reach   beneath   the   inverted 
saucer  in  the  pan  of  water,  as  re- 
presented in  Fig.  2  ;  the  lower  end 
of  the  ignition-tube  should  be  about 
4  c.  m.  above  the  top  of  the  lamp. 
The  tube  may  be  supported  on  the 
iron  stand,  and  should  be  inclined 
as  represented  in  the  figure.     (For 
a  description  of  the  pneumatic  trough,  see  Appendix,  §  11.) 

Upon  heating  the  ignition-tube,  gas  will  begin  to  escape  from  the 
delivery-tube,  and  bubble  up  through  the  water.  The  first  portion  is 
simply  the  atmospheric  air  which  filled  the  tubes  at  the  beginning 
of  the  experiment,  and  which  is  expanded  by  heat.  This  air  may  be 
collected  in  a  small  bottle  by  itself,  and  thrown  away.  The  volume 
of  gas  thus  thrown  away  should  not  be  much  greater  than  that  of  the 
tubes.  As  the  ignition-tube  becomes  hotter,  gas  will  be  freely  given 
off  from  the  mercury  oxide  contained  in  it,  and  should  be  collected  in 
bottles  of  100  to  150  c.  c.  capacity. 

It  is  necessary  to  avoid  heating  intensely  any  single  small  spot  of 
the  ignition-tube,  lest  the  glass  soften,  and,  yielding  to  the  pressure 
from  within,  blow  outward,  and  so  spoil  the  tube  and  arrest  the  ex- 
periment. The  gas-flame  should  be  so  placed  and  regulated  as  to  heat 
3  or  4  c.  m.  of  the  tube  at  once. 

As  soon  as  the  disengagement  of  gas  slackens,  lift  the  iron  stand 
up,  and  take  the  delivery-tube  out  of  the  water,  taking  care  that  no 
water  remains  in  the  end  of  the  tube.  Then,  and  not  till  then,  extin- 
guish the  lamp.  (See  Appendix,  §  11.)  In  the  upper  part  of  the 
ignition-tube,  and  sometimes  in  the  delivery-tube  also,  metallic  mer- 
cury will  be  found  condensed  in  minute  globules.  The  liquid  metal 
is  volatile  at  the  temperature  to  which  it  has  been  subjected,  and  has 
distilled  away  from  the  hot  part  of  the  tube,  and  condensed  upon  the 
cooler  part. 

If  a  lighted  splinter  of  soft  wood  be  introduced  into  a  bottle  of  the 
gas  just  collected,  it  will  burn  with  much  greater  brilliancy  than  in 
the  air.  If  a  candle  which  has  just  been  extinguished  be  thrust,  while 
the  wick  still  glows,  into  another  bottle  of  the  gas,  the  glowing  wick  will 
burst  into  flame,  and  the  candle  will  burn  with  extraordinary  brightness, 


8  COMPOSITION  OF  AIR.  [§10. 

10.  It  is  very  obvious,  from  these  experiments,  that  the  gas 
which  enters  into  the  composition  of  mercury-rust  is  not  air 
itself ;  but,  since  it  came  originally  from  the  air,  if  it  is  not  the 
whole  of  air,  it  must  be  a  part  of  air.    It  has,  indeed,  been  found 
to  be  a  constant  constituent  of  the  air,  and  a  chemical  ele- 
ment of  very  various  powers  and  great  importance.     It  is  called 
oxygen,  and  under  this  name  will  form  the  subject  of  the  next 
chapter. 

11.  If  oxygen  be  not  air  itself,  but  only  a  constituent  of  air, 
it  follows  that  air  must  have  other  constituents,  or,  at  least,  one 
other  constituent.     If  mercury  be  heated  for  a  long  time   in 
contact  with  a  certain  confined  portion  of  air,  it  will  abstract 
from    this    air    all    of    the    oxygen,    and    there   will    be    left 
a   gas   differing   from   both    oxygen   and   common   air.      It   is 
unfit  for  the  support  of  combustion  and  of  animal  life  ;  a  candle 
is  instantly  extinguished  by  it,  as  if  plunged  in  water ;  and 
small  animals,  thrust  into  the  gas,  die  in  a  few  seconds.     The 
gas  is,  in  reality,  a  second  elementary  substance,  distinguished 
by  marked   chemical   and   physical   peculiarities.     It  is  called 
nitrogen,  and  under  this  name  will  be  more  completely  studied 
in  another  chapter. 

If  the  experiment  be  so  conducted  that  the  bulk  of  the  original  air, 
and  also  that  of  the  residual  nitrogen,  can  be  measured,  it  will  be 
found  that  the  latter  gas  occupies  four-fifths  as  much  space  as  the  air 
did  at  the  beginning  of  the  experiment.  Besides  oxygen  and  nitrogen, 
minute  quantities  of  two  or  three  other  gases  are  found  in  the  air, 
either  uniformly  or  occasionally  ;  but  the  amount  of  these  gases  is 
relatively  very  small,  and  they  will  not  be  considered  at  present. 

The  air,  then,  is  not  an  element,  but  is  a  complex  substance  ; 
and  its  two  principal  ingredients  are  the  elementary  bodies,  oxy- 
gen and  nitrogen,  mixed  in  the  proportion  of  four  measures  of 
nitrogen  to  one  of  oxygen. 


§  13.]  OXYGEN.  9 

CHAPTER   II. 
OXYGEN. 

12.  Oxygen  gas  may  be  obtained,  as  has  already  been  seen, 
by  heating  mercury  oxide  :  it  may,  however,  be  prepared  in  a 
variety  of  ways  ;  among  others,  and  very  conveniently,  by  heat- 
ing a  mixture  of  potassium  chlorate  and  manganese  binoxide, 

—  two  chemical  substances  whose  constitution  will  be  studied 
hereafter. 

Exp.  4.  —  Mix  intimately  5  grammes  of  potassium  chlorate  with  5 
grammes  of  "  black  oxide  of  manganese,"  which  has  been  previously 
well  dried.  Place  the  mixture  in  a  tube  of  hard  glass,  No.  1,  12  or 
15  c.  m.  in  length.  Attach  to  this  ignition-tube,  by  means  of  a  per- 
forated cork  or  caoutchouc  stopper,  a  delivery-tube  of  glass,  No.  7,  as 
represented  in  Fig.  2,  and  described  upon  page  7.  Heat  the  mixture  in 
the  ignition-tube,  and  collect  the  gas  which  will  be  given  off  in  bottles 
or  jars  of  the  capacity  of  about  250  c.  c.  The  first  100  c.  c.  or  so  of  gas 
should  be  rejected,  since  it  will  be  contaminated  with  the  air  originally 
contained  in  the  apparatus. 

In  performing  this  experiment,  the  following  precautions  should  be 
observed.  1.  Both  the  potassium  chlorate  and  the  manganese  bin- 
oxide  should  be  perfectly  dry  and  pure  ;  that  is,  free  from  moisture, 
dust  or  particles  of  organic  matter.  2.  As  soon  as  the  oxygen  begins 
to  be  delivered,  the  heat  beneath  the  ignition- tube  should  be  dimin- 
ished, if  need  be,  and  so  regulated  that  the  evolution  of  gas  shall  be 
tranquil  and  uniform.  3.  The  uppermost  portions  of  the  mixture 
should  be  heated  before  the  lower.  4.  The  ignition-tube  should  never 
be  filled  to  more  than  one-third  its  total  capacity,  lest  particles  of  solid 
matter  be  projected  into  the  delivery-tube,  and  the  outlet  for  the  gas 
be  thus  stopped.  5.  The  ignition-tube  should  always  be  inclined  as 
represented  in  Fig.  2,  and  never  placed  upright  in  the  flame. 

1 3.  Oxygen  is  a  transparent  and  colorless  gas,  not  to  be  dis- 
guished  by  its  aspect  from  atmospheric  air.     Like  air,  it  has 
neither   taste   nor   smell.      It   is,    however,    somewhat    heavier 
than  air.     If  the  weight  of  a  measure   of  air  be  taken  as  1, 


10  OXYGEtf  SUPPORTS  COMBUSTION.  [§  14. 

then  the  weight  of  the  same  measure  of  oxygen  is  found  to  be 
1.1056.  One  of  its  most  striking  characteristics  is  its  power 
of  making  things  bum.  This  has  been  already  illustrated  in 
Exp,  3,  §  9, 

If  a  piece  of  phosphorus  the  size  of  a  small  pea,  having  been  well 
dried  between  pieces  of  blotting-paper,  is  placed  in  a  deflagrating- 
spoon,  touched  with  a  hot  wire  or  a  lighted  match,  and  then  thrust 
into  a  jar  of  oxygen,  it  will  burn  with  intense  brilliancy,  and  with  the 
formation  of  a  dense  white  smoke.  The  following  experiments  will 
•  still  further  illustrate  this  property  of  oxygen  :  — 

Fig.  3.  Exp.  5.  —  Place  in  a  deflagrating-spoon  (see  Appendix, 
§  13)  a  bit  of  sulphur  as  large  as  a  pea.  Light  the  sulphur, 
and  thrust  it  into  a  bottle  of  oxygen.  It  will  burn  with  a 
beautiful  blue  flame,  and  much  more  brilliantly  than  in  air. 
A  suffocating  gas  is  at  the  same  time  produced. 

Exp.  6.  —  Place  a  piece  of  charcoal  —  that  of  bark  is  best 
—  in  a  deflagrating-spoon.  Kindle  the  charcoal  by  holding  it 
in  the  flame  of  a  lamp,  and  then  introduce  it  into  a  bottle  of 
oxygen.  It  will  burn  vividly,  throwing  off  brilliant  sparks 
if  bark-charcoal  had  been  employed.  In  this  experiment,  as  in  the 
preceding,  the  products  of  the  combustion  are  obviously  gaseous,  no 
solid  substance  being  formed. 

Many  substances  commonly  called  incombustible  because  they  do  not 
burn  readily  in  ordinary  air,  burn  vigorously  in  oxygen.  Of  these,  me- 
Fig.  4.  tallic  iron  may  be  taken  as  an  example.  A  watch-spring,  which 
has  been  rendered  flexible  by  igniting  it  and  allowing  it  to 
cool  slowly,  is  made  into  a  spiral  coil,  and  to  the  end  is  at- 
tached a  bit  of  tinder  or  of  twine  soaked  in  sulphur.  If  the 
kindling-material  be  lighted,  and  the  spiral  then  plunged  into 
a  jar  of  oxygen,  the  iron  will  burn  brilliantly  with  scintillation. 
From  time  to  time,  glowing  balls  of  molten  matter  fall  off  from 
the  wire,  and  bury  themselves  in  the  layer  of  sand  which 
should  have  been  placed  at  the  bottom  of  the  bottle. 

14.  It  is  thus  clearly  proved  that  iron,  when  red-hot,  com- 
bines with  oxygen.  It  is  the  burnt  or  oxidized  iron  which  falls 
in  globules  to  the  bottom  of  the  bottle.  The  compounds  which 
are  formed  by  the  union  of  oxygen  with  other  elements  are  called 
oxides.  The  substances  which  have  been  heretofore  mentioned 


17."] 


OXtDAftOX. 


under  the  more  familiar  name  of  rust,  like  iron-rust,  tin-rust, 
mercury-rust,  are  called,  in  chemistry,  oxides  ;  as  iron  oxide,  tin 
oxide,  mercury  oxide. 

15.  The  most  important  quality  of  oxygen  is,  that,  with  a 
single  exception,  it  unites  with  all  the  other  elements  to  form 
compounds  which  are  sometimes  solid,  as  in  the  case  of  iron, 
and   sometimes   gaseous,   as  in  the  case  of   sulphur  (Exp.   5). 
(  Oxygen  is  the  most  widely  diffused  and  the  most  abundant  of 
all  known  substances.     Not  only  does  it  constitute  about  one- 
fifth  the  volume  of  the  air,  but  at  least  one-third  of  the  solid 
i  crust  of  the  globe  is  composed  of  it.     It  is  the  chief  ingredient 
i  of  water,   as  will  appear  in  a  subsequent  chapter.     Silica,  in 
all  its  varieties  of  sand,  flint,  quartz,  rock-crystal,  etc.,  contains 
about  half  its  weight  of  oxygen  ;  and  the  same  is  true  of  the 
various  kinds  of  clay,  and  of  chalk,  limestone  and  marble.     It 
(enters  largely  into  the  composition  of  plants  and  animals,  and 
is  absolutely  essential  to  the  maintenance  of  animal  and  vege- 
table life. 

16.  The  combination  of  oxygen  with  various  substances  is 
often  accompanied  by  the  development  of  light  and  heat,  as  in 
Exps.  5  and  6.     All  the  ordinary  phenomena  of  fire  and  light 
which  we   daily  witness  depend  upon  the  union  of  the  body 
burned  with  the  oxygen  of  the  air.     Indeed,  the  term  combus- 
tion may,  for  all  ordinary  purposes,  be  regarded  as  synonymous 
with  oxidation. 


CHAPTER  III. 
NITROGEN. 

17.  The  simplest  method  of  preparing  nitrogen  is  to  burn 
out  the  oxygen  from  a  confined  portion  of  air,  by  phosphorus  or 
by  a  jet  of  hydrogen. 


12  PREPARATION  OF  NITROGEN.  [§  18. 

Exp.  7.  —  Into  a  small  porcelain  capsule,  supported  on  a  piece 
of  stout  iron  wire  bent  as  represented  in  Fig.  5,  put  about  a  cubic 
centimetre  of  phosphorus,  and  set  it  on  fire.  Invert  over  the  capsule 
5.  a  wide-mouthed  bottle,  of  the  capacity 

of  a  litre  or  more,  and  hold  this  bottle 
so  that  its  mouth  shall  dip  beneath 
the  surface  of  the  water.  During  the 
first  moments  of  the  combustion,  the 
heat  developed  thereby  will  cause  the 
air  within  the  bottle  to  expand  to  such 
an  extent,  that  a  few  bubbles  of  the  air 
will  be  expelled  ;  but,  after  several  sec- 
onds, water  will  rise  into  the  bottle  to 
take  the  place  of  the  oxygen,  which  has  united  with  the  phosphorus. 

The  dense  white  cloud  which  fills  the  bottle  at  first  is  a  compound 
of  phosphorus  and  oxygen,  which  is  soluble  in  water.  It  will,  there- 
fore, soon  be  absorbed  by  the  water  in  the  pan,  and  will  disappear  ;  so 
that  at  the  close  of  the  experiment  nearly  pure  nitrogen  will  be  left 
in  the  bottle.  But,  as  the  phosphorus  ceases  to  burn  before  the  last 
traces  of  oxygen  are  exhausted,  the  nitrogen  obtained  by  this  method 
is  never  absolutely  pure. 

Remove  the  wire  with  the  capsule,  which  may  be  readily  done  by 
tipping  the  bottle  to  one  side,  taking  care  that  the  mouth  does  not 
come  out  of  the  water,  and  slip  a  glass  plate  under  the  mouth  of  the 
bottle  ;  invert  the  bottle  so  that  it  stands  upright,  and  thrust  a  burn- 
ing splinter  of  wood  or  a  lighted  candle  into  the  gas  ;  it  will  be  in- 
stantly extinguished. 

Nitrogen  may  also  be  prepared  by  passing  a  slow  stream  of  air  over 
bright  copper-turnings  heated  to  redness  in  a  hard  glass  tube.  The 
copper  combines  with  the  oxygen  of  the  air,  and  retains  it ;  while  the 
nitrogen  escapes  from  the  tube,  and  may  be  collected  over  water. 

18.  Nitrogen  is  a  transparent,  colorless,  tasteless,  odorless 
gas,  not  quite  as  heavy  as  air.  In  its  chemical  deportment 
towards  other  substances,  it  is  remarkably  unlike  oxygen. 
Whilst  oxygen  is  active  and,  as  it  were,  aggressive,  nitrogen, 
at  least  when  in  the  condition  in  which  it  exists  in  air,  is  re- 
markably inert  and  indifferent  as  regards  entering  into  combi- 
nation with  other  bodies.  It  is  marked  rather  by  the  absence 
of  salient  characteristics  than  by  any  active  properties  of  its 
own. 


§21.1  PROPERTIES  OF   WATER.  13 

As  it  extinguishes  flames,  so  it  destroys  life.  Animals  can 
not  live  in  an  atmosphere  of  pure  nitrogen.  It  is  not  poison- 
ous ;  if  it  were,  it  could  not  be  breathed  in  such  large  quanti- 
ties as  it  is  in  air.  An  animal  immersed  in  it  dies  simply  from 
want  of  oxygen. 

Nitrogen  is  widely  diffused  in  nature.  Besides  occurring 
in  the  air,  it  is  a  constituent  part  of  all  animals  and  vege- 
tables, and  of  many  of  the  products  resulting  from  their  de- 
composition. Notwithstanding  the  indisposition  of  nitrogen 
in  the  free  state  to  enter  into  combination,  a  very  large  num 
ber  of  interesting  and  important  compounds  can  be  formed  by 
resorting  to  indirect  methods  of  effecting  its  union  with  other 
elements. 


CHAPTER   IV. 
WATER. 

19.  Another  natural  substance,  quite  as   common  as  air,  is 
water.     Three-fourths  of  the  earth's  surface  is  covered  with  it. 
It  is  diffused  through  the  atmosphere  in  the  form  of  vapor,  and 
is  a  constituent  of  all  animal  and  vegetable  substances  and  of 
many  minerals.     We  take  up  next  this  familiar  substance,  in 
order  that  we  may  gain,  through  the  study  of  it,  a  deeper  insight 
into  chemical  principles,  and  enlarge  our  experience  by  making 
acquaintance  with  a  new  element. 

20.  At  the  ordinary  temperature  of  the  air,  pure  water  is  a 
transparent  liquid,  devoid  of  taste  or  smell.     In  thin  layers,  it 
appears  to  be   colorless  ;  but  large  masses  of  it  are  distinctly 
blue,  as  seen  in  mid-ocean,  in  many  deep  lakes  of  pure  water, 
and  in  masses  of  ice,  such  as  icebergs  and  some  glaciers,  where 
it  is  possible  to  look  through  the  ice  from  below. 

21.  At  4°,  the  temperature  at  which  it  is  densest,  water  is 
773  times  heavier  than  air  at  0°.     A  cubic  centimetre  of  water, 
at  this  temperature,  weighed  in  a  vacuum,  is  our  unit  of  weight, 


14  PROPERTIES  OP   WATER.  f§  22. 

—  a  gramme  \  therefore,  one  litre  of  water,  which  measures 
1,000  cubic  centimetres,  weighs  a  kilogramme. 

Pure  water  at  4°,  the  temperature  of  its  greatest  density,  is 
taken  as  a  standard  to  which  the  weights  of  equal  bulks  of  other 
substances,  liquid  or  solid,  are  referred.  In  other  words,  the 
specific  gravity  of  water  is  taken  as  1  ;  and  in  terms  of  this 
unit  the  specific  gravities  of  all  other  liquid  and  solid  substances 
are  expressed.  The  specific  gravity  of  gold,  for  example,  is  19.3  ; 
that  is  to  say,  the  weights  of  equal  bulks  of  water  and  of  gold 
are  to  one  another  as  1  to  19.3. 

22.  When  exposed  to  a  certain  degree  of  cold,  water  crystal- 
lizes with  formation  of  ice,  or  snow,  according  to  circumstances ; 
and,  upon  being  heated  sufficiently,  it  is  transformed  into  an 
invisible  gas,  called  steam.  Both  these  changes,  however,  are 
purely  physical  :  the  chemical  composition  of  the  water  is  the 
same,  whether  it  be  liquid,  solid  or  gaseous.  The  temperature 
at  which  ice  melts  is  one  of  the  fixed  points  of  the  centigrade 
thermometer,  numbered  0°,  and  the  temperature  at  which  w^ater 
boils,  under  a  pressure  of  760  m.  m.  of  mercury,  is  the  other 
fixed  point,  numbered  100°.  Water  evaporates  at  all  tempera- 
tures, and  is  therefore  a  constant  ingredient  of  the  atmosphere. 
Even  ice  slowly  evaporates,  at  temperatures  far  below  0°,  without 
first  passing  into  the  liquid  condition. 

In  crystallizing,  that  is  to  say,  in  assuming  the  solid  form, 
water  increases  in  volume.  From  this  fact  result  many  familiar 
phenomena,  such  as  the  floating  of  ice,  the  upheaving  and  disin- 
tegrating action  of  frost,  and  the  bursting  of  pipes  and  other 
hollow  vessels,  when  water  is  frozen  in  them. 

Steam  is  a  colorless,  transparent  gas,  as  invisible  as  atmos- 
pheric air,  and  considerably  lighter  than  it..  Wlien  steam  es- 
capes into  the  air,  it  is  partly  condensed  to  the  liquid  state  and 
there  is  formed  a  multitude  of  little  globules  precisely  similar  to 
the  minute  drops  of  water  which  make  up  ordinary  clouds  and 
fogs.  This  steam-cloud  is  sometimes  improperly  spoken  of  as 
steam  or  vapor,  an  error  against  which  the  student  should  be  on 
his  guard.  Similar  fogs  are  formed  whenever  the  atmosphere  is 


I  24.]  ANALYSIS  Of   WATER.  15 

cooled  to  a  temperature  so  low  that  the  aqueous  vapor  contained 
in  it  can  no  longer  exist  in  the  gaseous  state. 

Water  conducts  heat  very  slowly ;  it  may  even  be  boiled  for 
many  minutes  at  the  top  of  a  test-tube,  while  the  lower  end  of 
the  tube  is  held  in  the  fingers  without  inconvenience. 

23.  Let  us  now  pass  to  the  analysis  of  water.     Of  what  is 
water  composed1?     We   can  determine  this   point  by  methods 
similar  to  those  which  were  adopted  in  the  examination  of  air. 
At  a  low  red  heat  water  can  be  decomposed  by  several  of  the 
metals,  such  as  iron,   tin,  zinc  and   magnesium.     Iron  is  well 
adapted  for  this  purpose. 

If  water  be  boiled  in  a  suitable  flask,  and  the  steam  passed  through 
an  iron  tube  (a  piece  of  iron  gas-pipe  answers  very  well)  filled  with 
bright  iron-turnings,  and  heated  red-hot,  the  steam  is  decomposed  ; 
a  gas  escapes  from  the  tube,  and  may  be  collected  over  water.  On 
the  application  of  a  match,  the  gas  will  burn  with  a  pale  blue  flame. 
This  gas  is  one  of  the  constituents  of  water,  and  is  called  hydrogen. 
If,  after  the  tube  has  become  cold,  the  iron-turnings  be  removed,  they 
will  be  found  to  be  covered  with  a  black  coating  similar  to  that  which 
forms  on  iron  heated  in  the  air. 

24.  There  are  certain  metals  which  are  capable  of  decomposing 
water  without  the  application  of  heat.     The  metal  sodium  pos- 
sesses this  power. 

Exp.  8.  —  Make  a  small  cylinder  of  wire-gauze,  by  rolling  a  piece 
of  fine  gauze,  about  6  c.  in.  square,  around  a  thick  piece  of  No.  6 
glass  tubing.  Twist  fine  wire  around  the  cylinder,  in  order  to  pre- 
serve its  form  ;  then  slip  the  cylinder  off  the  glass,  and  close  one  end 
of  it  by  pressure  with  a  stout  pair  of  pincers.  Within  this  cylinder 
of  wire-gauze  place  a  piece  of  metallic  sodium  as  large  as  a  pea,  and 
then  close  the  upper  end  of  the  cylinder  by  pressure  with  the  pincers, 
as  before. 

Attach  the  wire-gauze  cage  firmly  Fis«  6« 

to  the  end  of  a  piece  of  stout  iron  wire 
and  thrust  it  quickly  into  the  water- 
pan,  so  that  the  cage  will  come  di- 
rectly under  the  mouth  of  a  small 
bottle  of  about  100  c.  c.  capacity, 
which  has  been  previously  filled  with 
water,  and  is  held  inverted  in  the 
pan  (Fig.  6). 


16 


ANALYSIS  OF   WATER. 


[§25. 


As  soon  as  the  water  comes  in  contact  with  the  sodium,  bubbles  of 
gas  will  begin  to  escape  from  the  wire-gauze  cage,  and,  passing  up 
through  the  water,  will  collect  at  the  top  of  the  inverted  bottle. 
When  the  evolution  of  gas  has  ceased,  close  the  mouth  of  the  bottle 
with  a  small  plate  of  glass,  turn  the  bottle  mouth  uppermost,  remove 
the  plate,  and  touch  a  lighted  match  to  the  gas.  The  gas  will  take 
fire  with  a  sudden  flash.  The  gas  is  hydrogen;  the  sodium  has 
united  with  the  other  constituent  (or  constituents)  of  the  portion  of 
water  decomposed,  and  the  new  compound  formed  is  dissolved  by  the 
water  in  the  pan. 

25.  By  these  experiments  it  has  been  proved  that  one  of 
the  components  of  water  is  a  gas  called  hydrogen.  But,  with 
ttie  exception  of  the  coating  upon  the  iron  alluded  to  in 
§  23,  we  have  as  yet  nothing  to  indicate  what  other  in- 
gredients the  water  may  contain.  Such  evidence  can,  how- 
ever, be  readily  obtained  by  resorting  to  another  method  of 
analysis. 

If  a  galvanic  current  is  caused  to  flow  through  water,  the  force  by 
Fig.  7.  which  the  constituents  of  the  water  are  held  together 
will  be  overcome,  and  the  wrater  will  be  resolved  into 
the  elements  of  which  it  is  composed.  On  immers- 
ing the  platinum  poles  of  a  galvanic  battery  in 
water,  to  which  a  little  sulphuric  acid  has  been 
added  for  the  purpose  of  increasing  its  conducting 
power,  minute  bubbles  of  gas  will  immediately  be 
given  off  from  these  poles,  and  will  be  seen  rising 
through  the  liquid.  If  the  apparatus  be  so  arranged 
that  we  can  collect  the  gas  given  off  from  each  pole 
in  a  test-tube  filled  with  water  to  which  a  little  sul- 
phuric acid  has  been  added,  it  will  be  found  that 
twice  as  much  gas  has  collected  in  the  one  tube  as  in 
the  other.  If  the  test-tube  containing  the  larger 
volume  of  gas  be  now  closed  with  the  thumb,  turned 
mouth  uppermost,  and  the  gas  within  touched  with  a 
lighted  match,  it  will  take  fire  and  burn  with  the  characteristic  flame 
of  hydrogen.  It  is,  in  fact,  hydrogen.  If  the  smaller  volume  of 
gas  in  the  other  tube  be  examined  in  the  same  way,  it  will  not  in- 
flame, although  it  gives  intense  brilliancy  to  the  combustion  of  the 
match.  If  a  splinter  of  wood,  retaining  but  a  single  ignited  spark,  be 


£  26.]  COMPOSITION  OF   WATER.  17 

immersed  in  the  gas,  it  instantly  exhibits  a  vivid  incandescence,  and 
in  a  moment  bursts  into  flame.  This  gas  is  oxygen. 

It  is  thus  proved,  that  out  of  water  may  be  unloosed  two  volumes 
of  hydrogen,  and  one  volume  of  oxygen.  It  remains  to  see  whether 
we  can  produce  water  from  a  mixture  of  oxygen  and  hydrogen.  If  we 
introduce  into  a  stout  test-tube  a  mixture  of  two  volumes  of  hydrogen 
and  one  volume  of  oxygen,  on  touching  a  lighted  match  to  the  mixed 
gas  it  instantly  explodes  with  great  violence,  the  hydrogen  burning 
suddenly,  so  that  for  a  moment  a  flash  of  flame  fills  the  whole  interior 
of  the  tube.  After  the  explosion,  water  will  be  found  deposited  as 
dew  upon  the  inner  walls  of  the  tube. 

At  the  temperature  of  the  air,  and  under  ordinary  circumstances, 
oxygen  and  hydrogen  do  not  combine  chemically.  Upon  being 
brought  together  they  simply  mix  with  one  another  mechanically,  in 
conformity  with  the  physical  laws  which  govern  the  diffusion  of  gases. 
But  under  the  influence  of  heat,  of  electricity  and  of  certain  other 
agents,  the  two  gases  will  unite  chemically,  and  will  thus  again  be 
converted  into  the  water  from  whence  they  were  derived. 

26.  We  have  thus  established  the  composition  of  water  by 
analysis,  having,  through  the  agency  of  the  electric  current, 
resolved  water  into  two  gaseous  constituents,  hydrogen  and 
oxygen ;  and  we  have  also  demonstrated,  by  the  converse  or 
synthetical  method,  that  hydrogen  and  oxygen  are  its  only 
constituents,  since  we  have  reproduced  water  by  effecting  the 
chemical  union  of  these  two  elementary  materials  mixed  in  due 
proportion.  There  is  one  important  point  in  the  combination 
of  these  elements  still  to  be  considered.  If  the  union  of  the 
hydrogen  and  oxygen  be  effected  in  an  apparatus  so  arranged 
that  the  water  formed  by  the  combination  is  kept  at  such  a  high 
temperature,  that  it  remains  in  the  gaseous  condition  under 
which  it  is  known  as  dry  steam,  it  is  found  that  the  two  vol- 
umes of  hydrogen  and  one  volume  of  oxygen  which  were  mixed 
together  have  become  compacted  by  uniting  chemically  into  two 
volumes  of  steam. 

If  equal  volumes  of  hydrogen  and  oxygen  be  represented  by 
equal  squares,  having  the  initials  of  the  elements  inscribed 
therein,  the  composition  of  water  by  volume,  and  the  condensa- 
2* 


4-     o     =      H2o 


18  ATOMS  AND  MOLECULES.  [§  27. 

tion  which  occurs  when  the  chemical  union  of  the   elements 
takes  place,  may  be  thus  expressed  to  the  eye  : 

Each  smallest  possible 
or  greatest  conceivable  vol- 
ume of  steam  will  invaria- 
bly yield,  on  decomposition, 
its  own  volume  of  hydro- 
gen, and  half  its  volume  of 
oxygen. 

27.  It  has  been  agreed  among  chemists  to  call  by  the  name 
molecule  the  least  quantity  of  a  compound,  or  of  an  elementary 
substance  which   can  exist  by  itself  uncombined,  or  take  part 
in  any  chemical  process.     The  smallest  conceivable  portion  of 
water  (which  by  this  definition  is  called  the  molecule)  like  any 
larger  quantity  of  water,  is  made  up  of  hydrogen  and  oxygen, 
and   if  decomposed    would   yield   twice  as   large  a  volume  of 
hydrogen  as  of  oxygen.     The  smaller  masses  of  matter  which 
make  up  the  molecules  are  called  atoms.     The  term  atom  may 
be  defined  as  the  smallest  quantity  of  an  element  which  can 
be  conceived  to  exist  in  combination.     A  molecule,  as  a  rule, 
contains  more  than  one  atom,  and  may  contain  a  great  number ; 
these  atoms  may  be  all  of  one  kind,  in  which  case  the  molecule 
is  that  of  a  simple  substance,  or  they  may  be  of  several  kinds,  as 
in  the  molecules  of  compound  substances. 

There  is  good  reason  to  believe  that  equal  volumes  of  the 
elementary  gases,  oxygen  and  hydrogen  (also  nitrogen  and  chlo- 
rine to  be  studied  hereafter)  contain  the  same  number  of  atoms. 
(See  §  140.)  If  this  be  true  there  will  be  in  the  molecule  of 
water  twice  as  many  atoms  of  hydrogen  as  of  oxygen,  because 
when  any  quantity  of  water  whatever  is  decomposed,  it  yields 
twice  as  much  hydrogen  by  volume  as  oxygen.  The  symbol 
H2O,  which  has  been  already  used  to  indicate  the  volumetric 
composition  of  water  (§  26),  may  also  be  used  to  indicate  the 
atomic  composition  ;  the  H2  will  represent  two  atoms  of  hydrogen, 
the  O  an  atom  of  oxygen,  and  the  H2O  a  molecule  of  water. 

28.  It  must  be  distinctly  borne  in  mind  that  as  to  the  abso- 


§  30.]  ATOMIC  WEIGHTS.  19 

lute  size  of  the  atoms,  we  know  nothing ;  the  same  thing  is 
true  with  regard  to  their  absolute  weight.  It  is,  however,  not 
difficult  to  determine  their  relative  weight.  If  we  take  the  case 
of  hydrogen  and  oxygen,  any  given  bulk  of  oxygen  weighs  16 
times  as  much  as  the  same  bulk  of  hydrogen,  and  as  there  are 
the  same  number  of  atoms  in  equal  bulks  of  these  two  gases, 
the  single  atom  of  oxygen  must  weigh  16  times  as  much  as  the 
single  atom  of  hydrogen.  The  numbers  1  and  1 6  are  called  the 
atomic  weights  of  hydrogen  and  oxygen,  respectively,  and  it  is 
possible,  although  not  always  by  the  same  method,  to  determine 
the  relative  weights  of  the  atoms  of  all  the  elements.  The 
atomic  weight  is,  in  each  case,  referred  to  that  of  hydrogen, 
which  is  called  1. 

If  the  atomic  weights  of  hydrogen  and  oxygen  be  borne  in 
mind,  the  symbol  of  water,  H2O,  will  now  remind  us  of  the  com- 
position of  water  by  weight,  for  as  each  molecule  of  water  is 
made  up  of  two  atoms  of  hydrogen  and  one  atom  of  oxygen,  the 
proportion  by  weight  in  which  these  two  elements  are  combined 
together  will  be  as  2  to  16,  or  as  1  to  8. 

29.  Having  thus  succeeded  in  determining  the  constituents 
of  air  and  water,  we  are  naturally  led  to  inquire  whether  it  be 
not  possible  to  resolve  oxygen,  nitrogen  and  hydrogen  themselves 
into  simpler  forms  of  matter.     To  this  question  but  one  answer 
can  be  made,  namely,  that  oxygen,  nitrogen  and  hydrogen  are 
incapable  of  decomposition  by  any  means  as  yet  at  our  disposal. 
We  are,  therefore,  justified  in  regarding  these  gases  as  simple 
bodies,  or  elements,  in  contradistinction  to  decomposable  bodies, 
such  as  air  and  water. 

30.  The  water  which  occurs  in  nature  is  never  absolutely 
pure.     In  the  form  of  ice,  and  as  it  falls  from  the  clouds  as 
rain   or   snow,   it   is,   indeed,   tolerably  free  from  foreign  sub- 
stances ;  but,  after  having  once  soaked  into  the  ground,  it  be- 
comes charged  with  a  variety  of  mineral  and  other  substances, 
which,  being  soluble  in  water,  are  dissolved  by  it  as  it  trickles 
through  the  earth. 

Where  the  proportion  of  soluble  matter  contained  in  the  water 


20  DISTILLATION.  [§  3| 

is  unusually  large,  and  particularly  if  it  possesses  marked  medi- 
cinal properties,  the  water  is  called  mineral  water,  and  the  springs 
from  which  it  issues  are  known  as  mineral  springs.  Sea-water 
may  be  regarded  as  a  variety  of  mineral  water. 

31.  For  the  conduct  of  chemical  investigations,  it  is  often 
necessary  to  purify  natural  water.     This  is  done  by  a  process 
called  distillation.   As  a  general  rule,  distilled  water  is  employed 
in  all  delicate  chemical  operations. 

Exp.  9.  —  In  a  retort  of  500  c.  c.  capacity,  put  200  or  300  c.  c*.  of 
well-water.  Thrust  the  neck  of  the 
retort  into  a  half-litre  receiver  placed  in 
a  pan  of  cold  water.  Cover  the  re- 
ceiver with  a  cloth  or  with  coarse  paper, 
and  upon  this  pour  cold  water  from 
time  to  time,  or  pile  upon  if  fragments 
of  ice.  Place  the  retort  upon  wire- 
gauze,  on  a  ring  of  the  iron  lamp-stand, 
and  adjust  the  distance  of  the  retort 
from  the  lamp  as  described  in  Exp.  3, 
Fig.  2.  Light  the  lamp  beneath  the  retort,  and  bring  the  water  to 
boiling.  As  fast  as  the  water  in  the  retort  is  converted  into  steam, 
this  vapor  will  pass  over  into  the  cold  receiver,  and  will  there  be  con- 
densed again  to  the  liquid  condition.  Continue  to  boil  until  about 
three-quarters  of  the  water  in  the  retort  has  evaporated. 

The  earthy  and  saline  ingredients  of  well-water  are  for  the  most 
part  not  volatile  :  very  few  of  them  are  capable  of  accompanying  the 
water  as  it  goes  off  in  vapor  ;  hence  the  greater  part  of  the  original 
impurity  of  the  water  will  remain  behind  in  the  retort. 

Exp.  9  a.  —  Place  a  few  drops  of  the  distilled  water  obtained  in 
the  preceding  experiment  upon  a  piece  of  platinum-foil  (Appendix, 
§  14).  Hold  the  foil  with  iron  pincers  above  the  gas-flame  in  such  a 
manner  that  the  liquid  may  slowly  evaporate  without  boiling  or 
spirting.  After  the  water  has  disappeared,  no  residue  will  be  found 
upon  the  foil.  Take  now  the  same  number  of  drops  of  water  from 
out  the  retort,  and  evaporate  them  upon  the  foil  as  before.  A  very 
decided  residue  of  earthy  matter  will  be  left  upon  the  foil. 

32.  In  the  operation   of  distillation,   the   substance   to    be 
distilled  must  in  the  first  place  be  converted  into  the  condition 


§  33.]  WATER  DISSOLVES  GASES.  21 

of  vapor  ;  this  vapor  must  next  be  transferred  to  another  vessel, 
and  there,  by  refrigeration,  be  again  condensed  to  the  liquid 
state.  As  will  appear  from  the  foregoing  experiment,  the 
vaporization  is  effected  in  the  retort  or  still,  and  the  refrigera- 
tion in  the  condenser.  In  the  experiment  above  given,  the 
receiver  acts  at  once  as  receiver  and  condenser ;  but  in  many 
cases  it  is  better  to  interpose  a  cooling-apparatus  between  the 
retort  and  the  receiver.  A  convenient  form  of  such  apparatus, 
known  as  Liebig's  condenser,  is  arranged  so  that  the  vapor  to 
be  condensed  must  pass  into  a  long  tube  which  is  kept  cool  by 
being  enclosed  in  a  larger  tube  through  which  cold  water  is  made 
to  circulate.  A  figure  representing  such  a  condenser  will  be 
found  011  page  146. 

33.  The  mineral  and  other  substances  alluded  to  above  are 
not  the  only  impurities  of  natural  water.  It  contains  also  oxygen 
and  nitrogen  in  solution,  as  both  of  these  gases,  which  are  present 
in  the  air,  are  somewhat  soluble  in  water.  That  water  does 
actually  contain  dissolved  gases  may  be  shown  by  the  following 
experiment. 

• 

Exp.  10.  —  By  means  of  a  sound  perforated  cork  or  caoutchouc 
stopper,  adapt  to  a  flask  of  the  capacity  of  1  or  2  litres  a  gas-delivery 
tube,  No.  6,  long  enough  to  reach  to  the  water-pan  in  the  usual  way. 
Upon  the  outer  end  of  the  delivery-tube  tie  a  short  piece  of  caoutchouc 
tubing,  to  which  a  stopper  made  of  a  bit  of  glass  rod,  or  a  wooden 
plug,  has  been  fitted.  Fill  the  flask  completely  with  ordinary  well  or 
river  water ;  fill  also  the  delivery-tube  with  water,  and  close  it  by 
putting  the  stopper  in  the  caoutchouc  tube.  Carefully  place  the  cork 
of  the  delivery-tube  in  the  neck  of  the  flask  in  such  manner  that  no 
air  shall  be  entangled  by  the  cork  ;  at  the  same  moment  remove  the 
plug  from  the  delivery-tube,  and  finally  press  the  cork  firmly  into  the 
flask.  Both  flask  and  tube  will  now  be  completely  full  of  water. 
Place  the  dried  flask  upon  a  ring  of  the  iron  stand,  and  invert  a  bottle 
filled  with  water  over  the  end  of  the  delivery-tube.  Now  slowly 
bring  the  contents  of  the  flask  to  boiling. 

As  the  water  gradually  becomes  warm,  numerous  little  bubbles  of 
gas  will  be  seen  to  separate  from  the  liquid,  and  to  collect  upon  the 
sides  of  the  flask  ;  these  subsequently  coalesce  to  larger  bubbles, 
which  collect  in  the  neck  of  the  flask.  As  soon  as  the  water  actually 


22  SOLUTION.  [§  34. 

boils,  the  steam  will  force  this  gas  out  of  the  flask,  and  it  will  collect 
in  the  inverted  bottle  at  the  end  of  the  delivery-tube,  the  steam  being 
meanwhile  condensed  as  fast  as  it  conies  in  contact  with  the  cold  water 
in  the  pan.  By  continuing  to  boil  moderately  during  ten  or  fifteen 
minutes,  nearly  all  the  gas  can  be  swept  out  from  the  flask  by  means 
of  the  escaping  steam.  The  delivery-tube  may  then  be  lifted  from 
the  water-pan  and  the  lamp  extinguished.  As  to  the  exact  character 
of  the  gases  thus  collected  we  shall  learn  something  in  a  subsequent 
chapter. 

34.  As  might  be  inferred  from  the  foregoing,  water  has*  the 
property  of  dissolving  many  substances,  solid,  liquid  and  gas- 
eous. Sugar,  for  example,  dissolves  readily  in  water ;  but  sand 
is  insoluble  therein.  A  substance  is  said  to  be  soluble  in  water 
when  it  is  capable  of  being  divided  in  and  dispersed  through 
the  water  so  intimately  and  completely  that  its  particles  become 
invisible,  and  can  no  longer  be  separated  by  filtration ;  the 
result  of  this  coalescence,  or  the  solution  as  it  is  termed,  is  a 
transparent  liquid,  as  a  general  rule  scarcely  less  mobile  than  the 
water  itself. 

Of  the. various  substances  soluble  in  water,  some  dissolve  in 
far  larger  proportion  than  others.  With  some  liquids,  as  alcohol 
for  example,  water  can  be  mixed  in  any  proportion  ;  but  of 
ether  it  dissolves  but  little,  and  of  oil  none.  The  proportion 
of  any  substance  that  can  be  dissolved  in  a  given  quantity  of 
water  is  usually  limited,  and,  under  fixed  conditions,  is  definite 
and  peculiar  for  each  substance.  When  a  given  quantity  of 
water  has  dissolved  as  much  of  a  substance  as  it  is  capable  of 
dissolving  at  the  temperature  and  pressure  to  which  it  happens 
to  be  exposed,  the  solution  is  said  to  be  saturated.  Of  nearly 
all  solid  substances,  hot  water  dissolves  a  greater  quantity  than 
cold  water :  gases,  however,  are  less  soluble  in  hot  than  in  cold 
water,  as  already  illustrated  by  Exp,  10. 


§  35.]  HYDROGEN.  23 


CHAPTEE  V. 
HYDROGEN. 

35.  The  commonest  method  of  preparing  hydrogen  is  by 
treating  zinc  or  iron  with  sulphuric  or  muriatic  acid.  Unless 
very  large  quantities  of  the  gas  are  needed,  this  method  is  much 
more  convenient  than  either  of  those  heretofore  mentioned. 

Exp.  11.  —  To  a  bottle  18  or  20  c.  m.  high,  and  of  500  or  600  c.  c. 
capacity,  the  mouth  of  which  has  an  internal  diameter  of  2.5  to  3  c.  m., 
fit  a  caoutchouc  stopper  or  a  Fig.  9. 

sound  cork,  furnished  with 
a  thistle-tube,  Fig.  9,  and  a 
gas  delivery-tube,  of  No.  6 
glass.  Within  the  bottle  put 
15  or  20  grms.  of  granulated 
zinc,  or  small  scraps  of  the 
sheet  metal,  and  as  much 
water  as  will  fill  about  one- 
quarter  of  the  bottle.  Replace 
the  cork  in  the  bottle,  taking 
care  to  press  it  in  tightly, 
and  gradually  pour  in  com- 
mon muriatic  acid  through 
the  thistle-tube.  The  thistle-tube  must  reach  nearly  to  the  bottom 
of  the  bottle,  so  that  its  point  may  dip  Beneath  the  water  ;  and  the 
muriatic  acid  must  be  added  by  small  successive  portions,  —  not  more 
than  a  large  thimbleful  at  a  time. 

On  the  addition  of  the  first  portions  of  the  acid,  chemical  action 
will  ensue,  the  contents  of  the  bottle  will  become  warm,  and  gas  will 
be  seen  to  escape  from  the  liquid.  This  gas  is  hydrogen. 

After  all  the  air  has  been  expelled  from  the  bottle,  the  hydrogen 
may  be  collected  over  the  water-pan,  in  inverted  bottles  filled  with 
water.  The  moment  at  which  the  hydrogen  ceases  to  be  contaminated 
with  air  can  be  determined  by  collecting  small  portions  of  the  escap- 
ing gas  in  wide-mouthed  bottles  of  about  50  c.  c.  capacity,  and  testing 
its  quality  by  means  of  a  lighted  match.  In  doing  this  the  small 


24  CHEMICAL  SYMBOLS.  [§  36. 

bottle  filled  with  gas  must  not  be  turned  over,  but  should  be  carefully 
lifted  from  the  water  without  changing  its  vertical  position,  and  the 
lighted  match  should  then  be  applied  to  the  mouth  of  the  bottle. 
If  the  hydrogen  be  pure,  it  will  burn  tranquilly  at  the  mouth  of  and 
within  the  bottle  ;  but,  in  case  the  gas  is  still  mixed  with  much  air,  a 
sharp  explosion  will  occur  at  the  moment  when  the  match  is  touched 
to  it.  In  experimenting  with  hydrogen,  no  light  should  ever  be 
brought  into  contact  with  the  contents  of  the  bottle  in  which  it  is 
generated,  or  with  any  large  quantity  of  the  gas,  until  the  purity  of 
the  sample,  or  rather  its  non-explosive  character,  has  been  demon- 
strated by  applying  to  a  very  small  volume  of  the  gas  the  test  above 
described. 

This  experiment,  which  has  here  been  executed  with  zinc,  can  be 
equally  well  performed  with  iron-filings,  and  with  several  other  of  the 
less  common  metals. 

36.  "We  now  proceed  to  study  the  chemical  action  which 
takes  place'  in  the  above  experiment.  The  muriatic  acid,  or,  in 
chemical  language,  chlorhydric  acid,  which  was  employed, 
is,  in  reality,  a  solution  in  water  of  a  very  soluble  gaseous  sub- 
stance, to  which  the  name  chlorhydric  acid  is  more  strictly 
applied.  This  gaseous  substance,  the  pure  chlorhydric  acid,  is 
a  chemical  compound  of  the  element  hydrogen  and  of  another 
element,  called  chlorine,  which  will  shortly  be  described. 
The  compound  may  be  represented  by  the  symbol  HC1, 
in  which  H  represents,  as  before,  the  least  proportional  weight 
of  hydrogen  which  exists  in  combination,  and  Cl  the  least  pro- 
portional weight  of  chlorine.  We  may  likewise  abbreviate  the 
word  zinc  to  the  symbol  Zn ;  and  the  chemical  process,  or  reac- 
tion, by  which  the  hydrogen  is  liberated,  may  then  be  symbolized 
by  the  equation,  — 

2  HC1  +  Zn  =  ZnCl2  -f  2  H. 

Since  hydrogen  is  gas,  it  escapes  as  such,  and  there  remains 
dissolved  in  the  water  within  the  bottle  a  compound  of  the 
elements  chlorine  and  zinc,  called  zinc  chloride.  The  zinc, 
which  was  free,  enters  into  combination,  and  the  hydrogen, 
which  was  in  combination,  is  set  free  j  in  other  words,  the 
zinc  has  been  substituted  for,  or  has  replaced,  the  hydro- 
gen. 


§  36.]  CHEMICAL  SYMBOLS.  24« 

It  may  here  be  stated  that  chemists  of  all  nations  have  agreed  to 
represent  each  of  the  elements  by  a  symbol  which  consists  either  of 
the  initial  letter  of  the  Latin  name  of  the  element,  or,  when  the 
names  of  two  or  more  of  the  elements  begin  with  the  same  letter,  of 
the  initial  letter,  together  with  the  tirst  of  the  succeeding  letters  in 
the  Latin  name,  which  is  distinctive.  Thus  Fe  (Ferrum)  is  the 
symbol  of  iron,  C  of  carbon,  Ca  of  calcium,  Cl  of  chlorine,  and  Cr 
of  chromium.  These  symbols  do  not  serve  simply  as  abbreviations, 
but  each  stands  for  a  single  atom  of  the  element  indicated  ;  if  we 
know  the  atomic  weight  of  the  element,  the  symbol  may  stand  to  us 
also  for  a  certain  definite  weight  of  the  element  in  question,  as  we  have 
seen  in  §  26.  In  the  same  section  the  symbols  O  and  H  were  used 
to  indicate  one  volume  of  oxygen  and  hydrogen,  respectively  :  this 
use  of  the  symbols  to  express  volumetric  relations  is,  however,  not 
the  same  for  all  the  elements,  and  it  will  be  treated  of  in  Chapter  XI. 

A  group  of  these  elementary  symbols  just  described,  written  to- 
gether, stands  for  a  molecule  made  up  of  the  atoms  indicated.  Thus 
HC1  stands  for  a  molecule  containing-  one  atom  of  hydrogen  and 
one  atom  of  chlorine  ;  ZnCl2  stands  for  a  molecule  made  up  of  one 
atom  of  zinc  and  two  atoms  of  chlorine  ;  the  figure  2  written  below 
the  line  applies  to  the  Cl  alone.  If  the  figure  2  were  written  on  the 
line,  and  before  the  symbol,  it  would  indicate  two  molecules  of  the 
compound  ;  as  2  HC1.  The  knowledge  of  the  atomic  weights  enables 
us  to  use  the  molecular  symbols  to  express  the  composition  of  a 
substance  by  weight  ;  thus  we  have  already  seen  (§  26)  that  H2O 
indicates  that  in  every  18  parts  by  weight  of  water  there  are  16 
parts  by  weight  of  oxygen,  and  2  parts  by  weight  of  hydrogen. 
In  the  same  way,  knowing  the  atomic  weight  of  chlorine  to  be 
35.5,  from  the  symbol  HC1  we  learn  that  in  every  36.5  parts 
by  weight  of  chlorhydric  acid  there  are  35.5  parts  by  weight  of 
chlorine,  and  1  part  by  weight  of  hydrogen.  We  say  the  molec- 
ular weight  of  water  is  18,  and  the  molecular  weight  of  chlorhy- 
dric acid  is  36.5,  meaning  that  the  molecule  of  water  weighs  18 
times,  and  the  molecule  of  chlorhydric  acid  36.5  times  as  much  as 
the  atom  of  hydrogen,  which  is  taken  as  the  unit  of  molecular  as 
well  as  of  atomic  weight.  The  circumstances  under  which  we  may 
also  learn  the  volumetric  composition  of  a  compound  from  the  symbol 
of  its  molecule,  will  be  discussed  hereafter.  (See  page  291.) 

Every  well-understood  chemical  action   may  be  expressed  as  an 
equation.      The   one  just  given,  2  HC1  -f  Zn  =  ZnCl2  +  2H, 


246  CHEMICAL  EQUATIONS.  [§  36. 

indicates  that  from  the  action  of  2  molecules  of  chlorhydric  acid  and 
1    atom   of  zinc    upon    each  other,  there  result  1  molecule  of  zinc 
chloride  and  2  atoms  of  hydrogen.     Of  course,  as  the  experiment  was 
actually  performed,  a  vast  number  of  molecules  of  chlorhydric  acid, 
and  the    corresponding   number  of  atoms  of   zinc,  acted  upon  each 
other, — the    equation    indicates    merely    the    relative    number.      It 
follows  naturally  from  the  very  conception  of  atoms  and  molecules, 
that  whenever  chemical  action  takes  place  between  two  bodies,  it  is 
always   between   fixed    and  definite    weights   of   those    two   bodies. 
Our  knowledge  of  the  atomic  weights  of  the  various  elements,  ena- 
bles us  to  calculate  from  the  equation  what  must  be  the  relative  pro- 
portion by  weight  of  the  substances  concerned  in  the  action.     The 
atomic  weight  of  zinc  is  65,  and  the  molecular  weight  of  chlorhydric 
acid  is  36.5,  and  the  equation  shows  us  that  for  every  atom  of  zinc 
weighing  65  of  our  units  of  weight  (the  unit  being  the  weight  of  an 
atom  of  hydrogen),  two  molecules  of  chlorhydric  acid  must  be  taken 
which  weigh  73  (i.  e.,  2    x  36.5)  of  these  same  units:    moreover, 
from  the  action  on  each  other  of  these  amounts  of  zinc  and  chlor- 
hydric acid,  there  are  formed  one  molecule  of  zinc  chloride,  weighing 
136  (i.  e.,  65  +  71),  and  two  atoms  of  hydrogen  weighing  2  of  these 
same  units.     It  is,  of  course,  immaterial  whether  the  unit  of  weight 
be  the  weight  of  an  atom  of  hydrogen,  or  a  pound,  or  a  kilogramme  ; 
the  relative  proportion,  according  to  which  these  two  substances  act 
upon  each  other,  must  in  every  case  be  the  same,  and  the  following 
proportions  will  hold  true  : — 

I  Weight  of  zinc  )  \  Weight  of  HC1 

(      in  any  case      \  \      in  same  case 

I  Weight  of  zinc  )      .      j  Weight  of  ZnCl3  )    =  65  •  136 
\      in  any  case     \  \      in  same-  case      ( 

If  the  weight  of  zinc  used  in  any  case  were  given,  the  weight  of 
chlorhydric  acid  required  could  be  readily  calculated,  as  we  should 
then  have  three  terms  of  a  proportion  given  to  find  the  fourth  ;  more- 
over, the  amount  of  zinc  chloride  produced  by  the  use  of  65  parts  of 
zinc  would  be  65  +  (2  x  35.5),  that  is,  136  parts  by  weight.  In  fact, 
if  the  amount  of  any  one  of  the  four  substances  were  given,  the 
amounts  of  the  other  three  could  be  found,  as  they  are  all  propor- 
tional. (See  also  §§  63  and  76.) 

It  is  also  to  be  remarked  that,  in  writing  the  equation,  no  account 
was  taken  of  the  water  in  which  the  HC1  was  dissolved.     This  water 


§  38.]  PROPERTIES  OF  HYDROGEN.  26 

remained  in  the  bottle  unchanged  after  the  experiment  was  finished, 
and  in  it  the  zinc  chloride  (ZnCl3)  formed  was  held  in  solution.  It 
would  be  possible  by  the  application  of  heat  to  evaporate  all  of  this 
water  and  leave  the  zinc  chloride  as  a  solid  substance. 

37.  Hydrogen  is  a  transparent,  colorless  and  tasteless  gas,  odor- 
less when  pure.    It  is  not  poisonous,  though  animals  die  from  suf- 
focation when  immersed  in  it,  as  they  do  in  an  atmosphere  of  nitro- 
gen.    It  is  the  lightest  substance  known ;  being  about  14 J  times 
lighter  than  air,  11,160  times  lighter  than  water,  and  151,700 
times  lighter  than  quicksilver.     Hydrogen  is  the  standard  of 
specific  gravity  for  gases,  as  water  is  for  liquids  and  solids ;  its 
specific  gravity  is  therefore  unity. 

38.  The  exceeding  lightness  of  hydrogen  can  be  illustrated 
by  filling  soap-bubbles  with  the   gas.     They  will  rise  rapidly 
through  the  air  ;  and,  if  touched  with  a  lighted  taper,  the  hydro- 
gen will  immediately  burst  into  flame.     Owing  to  its  lightness 
hydrogen  can  readily  be  poured  or  decanted  upwards  from  one 
vessel  to  another. 

Exp.  12.  —  Lift  from  the  water-pan  a  thick,  strong,  wide-mouthed 
bottle,  of  200  to  300  c.  c.  capacity,  full  of  hydrogen,  taking  care  to 
hold  it  in  a  perpendicular  position,  with  the  mouth  downward.  With 
the  other  hand  place  another  bottle  of  equal  size  and  strength,  but 
containing  only  air,  beside  the  hydrogen-bottle,  so  that  the  mouths  of 
the  bottles  shall  touch  at  one  edge.  Gradually  turn  down  the  hydro- 
gen-bottle, and  at  the  same  time  push  its  mouth  beneath  that  of  the 
air-bottle  in  such  manner  that  the  bottle  which  originally  contained 
the  hydrogen  shall  at  last  stand  upright  beneath  the  inverted  bottle. 
During  this  operation,  the  lighter  hydrogen  flows  up  into  the  upper 
bottle,  while  the  heavier  air  sinks  into  the  lower.  If  a  burning  match 
be  now  thrust  into  the  upper  bottle,  the  hydrogen  within  it  will  take 
fire  ;  but,  upon  applying  the  match  to  the  lower  bottle,  originally  full 
of  hydrogen,  there  will  be  found  in  it  nothing  but  air. 

Since  hydrogen  is  thus  lighter  than  air,  it  is  not  absolutely  neces- 
sary, in  collecting  it,  to  operate  over  water,  as  has  been  directed. 
When  a  gas  is  much  lighter  or  heavier  than  atmospheric  air,  it  may 
often  be  conveniently  collected  by  displacement.  A  bottle  can  be 
readily  filled  with  hydrogen  from  a  gas-holder  by  carrying  the  delivery- 


26  PROPERTIES  Of1  HYDROGEN.  [J  39. 

tube  to  the  top  of  the  inverted  bottle,  and  allowing  the  gas  to  flow  in. 
After  a  short  time  the  air  will  be  wholly  displaced,  and  the  bottle  filled 
with  hydrogen. 

39.  There  is  another  noticeable  peculiarity  of  hydrogen  which 
is  directly  connected  with  its  extreme  lightness.     It  possesses  in 
a  high  degree  the  power  of  diffusion.     This  diffusive  power  is  a 
physical  property  common  to  all  gases  and  vapors ;  in  the  case 
of  hydrogen,  it  is  only  the  intensity  of  the  diffusive  power  which 
is  remarkable.     The  following  experiment  will  serve  to  illustrate 
this  property. 

Exp.  13.  —  A  glass  tube,  3  or  4  c.  m.  in  diameter,  and  30  or  40  c.  m. 
long,  is  closed  at  one  end  with  a  plug  of  plaster  of  Paris  1  or  2  c.  m. 
Fig.  10.  thick.  The  tube  is  then  set  aside  for  a  day  or 
two,  in  order  that  the  plaster  may  become  dry- 
When  the  plug  is  dry,  fill  the  tube  with  hydrogen 
by  displacement,  and  set  it  upright  in  a  glass  of 
water.  Water  will  rise  rapidly  in  the  tube,  since 
hydrogen  escapes  through  the  plaster  more  rapidb 
than  air  can  enter  the  tube  through  this  porous  plug. 
If  the  tube  be  left  to  itself,  air  will  slowly  enter 
through  the  plaster,  so  that  the  water  within  the 
tube  will  in  due  time  sink  to  the  level  of  the  outside 
liquid. 

The  velocities  with  which  gases  diffuse  are  in  the  inverse  ratio  of 
the  square  roots  of  their  specific-  gravities.  Hence  it  happens  that 
hydrogen,  being  the  most  attenuated  of  all  gases,  diffuses  with  the 
greatest  rapidity.  Compared  with  that  of  oxygen,  its  rate  of  diffusion 
is  as  4  to  1  ;  that  is  to  say,  the  relative  rates  of  diffusion  of  the  two 
gases  are  inversely  as  the  square  roots  of  the  numbers  1  and  16,  which 
represent  the  specific  gravities  of  hydrogen  and  oxygen  respectively. 

On  account  of  its  high  diffusive  power,  hydrogen  can  be  kept 
only  in  perfectly  tight  vessels.  It  can  not  "be  kept  for  any  length 
of  time  in  bladders  or  rubber  bags,  and  it  will  leak  through  stop- 
cocks which  are  perfectly  tight  for  nitrogen  or  oxygen. 

40.  Hydrogen  is  exceedingly  inflammable,  as  has  been  already 
seen ;  that  is  to  say,  the  temperature  at  which  it  takes  fire  is 
comparatively  low.     But,  as  a  matter  of  course,  it  extinguishes 


Hi.] 


OX Y-tiYD&OGEN  BLO WPIPE. 


27 


any  burning  body  which  is  immersed  in  it,  since  oxygen  is  neces- 
sary for  the  support  of  combustion. 

Exp.  14.  —  Carefully  lift  from  the  water-pan  a  bottle  of  200  or 
300  c.  c.  capacity,  completely  full  of  hydrogen  ;  slowly  carry  the  bot- 
tle, the  mouth  of  which  is,  of  course,  held  downward,       Fig.  11. 
to  a  burning  candle  or  splinter  of  wood,  and  depress 
the  bottle  over  this  flame.     The  hydrogen  will  take 
fire  and  burn  below,  at  the  mouth  of  the  bottle,  where 
it  is  in  contact  with  the  oxygen  of  the  atmosphere  ; 
but  the  flame  of  the  candle  will  be  extinguished  the 
moment  it  becomes  completely  enveloped  by  the  hy- 
drogen.    The  candle  can  easily  be  relighted  by  slowly 
lifting  the  bottle  until  the  wick  is  brought  into  contact 
with  the  air  and  the  burning  hydrogen. 

41.  It. has  been  seen  that  the  hydrogen  flame  gives  but 
very  little  light ;  it  is,  however,  very  hot.  Indeed,  it  has  been 
found  that  when  a  given  weight  of  hydrogen  enters  into 
chemical  union  with  oxygen,  more  heat  is  developed  than  in 
the  burning  of  the  same  weight  of  any  other  substance.  On 
this  fact  depends  the  use  of  the  so-called  oxy-hydrogen  blow- 
pipe. 

Fig.  13. 


The  principle  of  the  construction  of  this  apparatus  may  be  learned 
from  Fig.  12.  It  consists  essentially  of  two  tubes,  one  within  the 
other.  The  inner  tube  (a)  is  connected  with  a  gas-holder  containing 
oxygen  ;  the  outer  tube  (&)  with  a  gas-holder  containing  hydrogen. 
The  cock  of  the  hydrogen  gas-holder  is  first  opened  and  the  hydrogen 
is  lighted  at  the  point  of  the  jet  ;  the  cock  of  the  oxygen  gas-holder 
is  then  slowly  opened  until  the  flame  is  reduced  to  a  fine  pencil.  A 
constant  and  sufficient  pressure  should  be  maintained  on  the  gas- 
holders. 


28  UNION  OF  HYDROGEN  AND  OXYGEN.  [§  42. 

In  the  flame  thus  produced,  a  fine  platinum  wire  will  readily  melt 
and  fall  into  drops.  The  intense  heat  of  the  oxy-hydrogen  flame  is 
thus  admirably  illustrated,  for  platinum  is  an  exceedingly  infusible 
metal,  which  can  scarcely  be  softened  in  the  hottest  furnace. 

If  a  piece  of  chalk  or  lime,  scraped  to  a  fine  point,  be  held  in  the 
flame  of  the  oxy-hydrogen  blow-pipe,  it  will  quickly  become  white- 
hot,  and  evolve  light  of  great  brilliancy,  almost  comparable  with  that 
of  the  sun.  On  this  principle  is  constructed  the  so-called  Drummond 
or  calcium  light,  often  employed  for  night-signals  and  optical  experi- 
ments. 

42.  No  matter  in  what  way  hydrogen  is  burned,  whether  in 
the  pure  state  or  in  combination  with  other  materials,  whether 
in  pure  oxygen  or  in  the  air,  the  product  of  the  combustion 
is  always  water.     At  the  high  temperature  of  the  flame,  this 
water  must,  of  course,  remain  in  the  condition  of  a  gas,  but  it 
can  readily  be  brought  to  the  liquid  state  by  reducing  the  tem- 
perature. 

Exp.  15.  —  Over  a  jet  of  burning  hydrogen,  best  obtained  from  a 
gas-holder,  hold  a  dry,  cold  bottle.  The  glass  soon  becomes  covered 
with  a  film  of  dew,  as  the  water  generated  by  the  union  of  hydrogen 
and  oxygen  condenses  in  droplets  upon  the  cold  sides  of  the  bottle. 

43.  If,  instead  of  burning  pure  hydrogen  as  it  flows  into  the 
air,  the  gas  be  first  mixed  with  oxygen,  and  then  ignited,  a  very 
different  result  will  be  obtained.     The  hydrogen  being  now  in 
contact  with  oxygen  at  all  points,  the  entire  mass  of  gas  will 
burn  with  a  violent  explosion  at  the  instant  when  a  light  is 
touched  to  it. 

This  may  be  illustrated  by  connecting  a  piece  of  glass  tubing  with 
Fig.  13.  a  gas-holder,  or,  better, 

a  rubber  bag,  containing 
a  mixture  of  2  volumes 
of  hydrogen  and  1  vol- 
ume of  oxygen.  The 
end  of  the  glass  tube  is 
dipped  into  a  dish  of 
soap-suds,  and  the  gas 
allowed  to  flow  until  a 


§  45.]  UNION  OF  HYDROGEN  AND  OXYGEN.  29 

mass  of  foam  not  too  large  has  formed  on  the  surface  of  the  suds.  If, 
after  the  removal  of  the  gas-holder,  the  foam  be  touched  with  a  long 
lighted  stick,  a  violent  explosion  will  occur. 

Care  should  be  taken  to  throw  away  any  remnant  of  the  mixture 
of  hydrogen  and  oxygen  which  may  have  been  left  in  the  gas-holder 
at  the  close  of  the  experiment,  and  upon  no  account  should  fire  ever 
be  brought  into  its  vicinity. 

The  loud  explosion  is  owing  to  the  fact  that  the  intense  heat 
emitted  at  the  moment  of  the  combination  of  the  two  gases 
expands  enormously  the  steam  formed  by  their  union.  As  the 
steam  is  immediately  condensed,  there  results  a  partial  vacuum, 
into  which  air  rushes  from  all  sides  ;  and  it  is  the  heavy  and 
sudden  undulations  thus  communicated  to  the  air  which  oc- 
casion the  noise.  The  outward  and  inward  shocks  follow 
one  another  so  quickly  that  the  ear  cannot  distinguish  between 
them. 

44.  Mixtures  of  hydrogen  and  air  produce  less  violent  explo- 
sions than  mixtures  of  hydrogen  and  oxygen,  because  of  the  inert 
nitrogen  in  the  air,  which  acts  as  an  elastic  pad  or  cushion  to 
break  the  force  of  the  shock. 

Exp.  16.  —  Introduce  2  volumes  of  hydrogen  and  5  volumes  of 
air  into  a  strong  round-bottomed  bottle,  such  as  is  used  for  soda- 
water.  Close  the  mouth  of  the  bottle  with  a  cork,  and  shake  vio- 
lently, in  order  that  the  gases  shall  be  mixed.  A  small  quantity  of 
water  should  be  left  in  the  bottle  to  act  as  a  stirrer.  Grasp  the  bottle 
firmly  in  one  hand,  remove  the  cork  with  the  .other,  and  apply  the 
open  mouth  pf  the  bottle  to  a  lighted  candle.  An  explosion  will  im- 
mediately ensue. 

45.  Since  air  is  everywhere  about  us,  and  since  all  ordinary 
combustions  occur  in  it,  it  has  become  customary  to  speak  of  it 
and  of  oxygen  as  supporters  of  combustion,  in  contradistinc- 
tion to   the  so-called  combustibles,  such  as  hydrogen.     These 
terms  are  often  convenient ;  but  that  they  have  only  a  relative, 
and  no  absolute  significance,  may  be  shown  experimentally,  as 

follows  :  — 

3* 


32  NITROGEN  PROTOXIDE.  [§  43 

nitrogen  and  oxygen ;  and  that,  as  in  the  case  of  water  two 
volumes  of  hydrogen  and  one  volume  of  oxygen  are  condensed 
into  two  volumes  of  dry  steam,  so  two  volumes  of  nitrogen  and 

one  volume  of  oxygen  are 
here  condensed  into  two 
volumes  of  this  transparent 
gas.  As  the  chemical  for- 


N 


N00 


mula  or  symbol  of  water  is 
H^O,  so  the  formula  of 
this  new  gas  is  N2O,  and  its  volumetric  composition  may  be 
represented  by  a  diagram  similar  to  that  by  which  we  conveyed 
to  the  eye  the  composition  of  water.  The  gas  is  called  nitrogen 
protoxide  or  nitrous  oxide.  The  equation  which  represents  the 
chemical  action  by  which  it  was  produced  may  be  thus  written  : 

NH4NO3  =  2H20  +  N20 

Ammonium  nitrate.  Nitrous  oxide. 

From  the  above  composition  by  volume,  and  from  the  known 
specific  gravities  of  nitrogen  and  oxygen,  the  composition  of 
nitrogen  protoxide  by  weight  is  readily  deduced.  The  specific 
gravity  of  nitrogen,  referred  to  hydrogen,  is  14  ;  that  of 
oxygen  1 6 ;  since  there  are  two  volumes  of  nitrogen  for  each 
volume  of  oxygen,  the  two  elements  must,  in  any  given  weight 
of  the  gas,  be  combined  in  the  proportion  of  28  parts  by 
weight  of  nitrogen  to  16  of  oxygen.  The  molecule  of  nitrogen 
protoxide,  N2O,  must  be  composed,  like  any  other  quantity  of 
the  gas,  of  28  parts  by  weight  of  nitrogen  and  16  of  oxygen; 
but,  precisely  as  in  the  case  of  water,  we  conceive  of  the 
molecule  as  made  up  of  two  atoms  of  nitrogen  and  one  atom 
of  oxygen ;  and  we  have  already  learned  that  if  the  atomic 
weight  of  hydrogen  be  represented  by  1,  that  of  oxygen  must 
be  16.  It  follows,  from  the  constitution  of  nitrogen  protoxide, 
that,  if  16  represents  the  smallest  proportional  weight  of  oxygen 
which  exists  in  combination,  14  must  be  the  corresponding 
smallest  weight  of  nitrogen  when  thus  united  with  oxygen. 
Mtrogen  protoxide  contains  £J,  or  36.36  per  cent,  of  oxygen. 


§50.] 


NITRIC  OXIDE. 


33 


Pig 


49.  Nitrous  oxide,   when  pure,  may  be  respired  for  a  few 
minutes  with  impunity.     When  inhaled,  it  produces  a  lively 
intoxication,  attended  with  a  disposition  to  muscular  exertion 
and  violent  laughter  ;  whence  its  trivial  name  of  laughing  gas. 
It  may,  however,  be  administered  so  as  to  cause  complete  insen- 
sibility to  pain ;  the  effect  lasts,  however,  for  only  a  very  short 
time.     It  is  advantageously  used  as  an  anaesthetic  in  such  sur- 
gical operations  as  can  be  performed  in  a  few  seconds. 

50.  Nitric  Oxide  (NO). — We  now  proceed  to  investigate 
another  compound  of  nitrogen  and  oxygen  which  may  be  pre- 
pared from  a  chemical  substance  with  which  we  shall  soon  be 
familiar,  nitric  acid. 

Exp.  19.— Place  15  or  20 
grms.  of  copper  turnings  or 
filings  in  a  bottle  arranged 
precisely  as  for  generating  hy- 
drogen (see  Experiment  11, 
§  35),  and  pour  about  25  c.  c. 
of  dilute  nitric  acid  made  by 
adding  to  the  common  strong 
acid  its  own  bulk  of  water. 
Brisk  action  will  immediately 
occur.  The  generator  be- 
comes filled  with  red  fumes 
which  gradually  disappear, 
and  when  the  gas  disengaged  is  collected  over  water,  it  is  found  to  be 
colorless.  Collect  three  bottles,  of  300  to  400  c.  c.  capacity  of  this 
gas,  adding  acid  from  time  to  time  as  may  be  necessary.  Save  the 
blue  solution  (copper  nitrate)  which  remains  in  the  generator  for 
future  use. 

Exp.  19a. — Dip  a  lighted  candle  into  a  bottle  of  the  gas.  The  light 
is  extinguished.  Into  the  same  bottle  thrust  a  glowing  splinter.  It 
will  not  inflame. 

Exp.  19b. — Lift  a  bottle  of  the  gas  from  the  water  so  that  air  may 
enter  the  bottle,  and  the  gas  may  escape  into  the  air.  Red  fumes,  of 
very  disagreeable  smell,  and  very  irritating  when  inhaled,  are  abun- 
dantly produced.  Bring  into  contact  with  these  fumes,  a  piece  of  mois- 
tened litmus-paper.  It  becomes  red  ;  the  significance  of  this  action 
will  appear  later. 


34  COMPOSITION  OF  NITRIC  OXIDE.  [§51. 

Exp.  19c. — Thoroughly  ignite  a  bit  of  sulphur  in  a  deflagrating- 
spoon,  and  introduce  it  into  a  bottle  of  the  gas.  It  will  not  burn. 
Into  the  same  bottle  thrust  a  piece  of  phosphorus  as  big  as  a  pea,  burn- 
ing actively.  The  combustion  will  be  continued  .with  great  bril- 
liancy. 

51.  By  the  preceding  experiments  we  learn  that  the  new  gas 
is  transparent  and  colorless,  and  that  it  differs  notably  from  all 
the  other  gases  thus  far  studied  in  its  relation  to  combustibles. 
Analysis  shows  that  the  gas  consists  of  nitrogen  and  oxygen, 
one  volume  of  each  gas  uniting  to  form  two  volumes  of  the 
compound  gas.  Its  molecule  will  be  represented  by  the  for- 
mula NO  ;  and  its  elements  are  united  by  weight  in  the  pro- 
portion of  14  parts  of  nitrogen  to  16  of  oxygen,  because  equal 
volumes  of  nitrogen  and  oxygen  weigh  respectively  1 4  and  1 6 
times  as  much  as  the  same  volume  of  hydrogen.  Its  com- 
position may  be  represented  by  the  accompanying  diagram. 
v v  The  «as  is  thus  another  ox- 


N 
14 


O 

16 


NO  30     I  ide  of  nitrogen  ;  it  is  gener- 

• —     -•  ally  known  as  nitric  oxide, 

but  some  regard  the  molecule  as  W2O2  and  name  the  compound 
nitrogen  binoxide. 

The  action  of  the  copper  on  the  nitric  acid  in  Exp.  19,  may 
be  represented  by  the  following  equation : — 

3Cu  +  8HN03  —  3CuN206  _j_  4HJ3  +  2NO. 

Copper.       Nitric  acid.        Copper  nitrate.  Nitric  oxide. 

When  the  same  element  unites  with  oxygen  in  more  than  one  pro- 
portion, the  compound  containing  a  single  atom  of  oxygen  in  the 
molecule  is  called  the  protoxide;  when  the  molecule  contains  two 
atoms  of  oxygen,  the  compound  is  called  the  linoxide ;  succeeding 
oxygen  compounds  would  be  the  teroxide,  quadroxide,  etc.  The  term 
peroxide  may  be  applied  to  any  compound  containing  more  oxygen 
than  the  protoxide,  although  if  there  are  several  such  oxides  it  is 
used  conventionally,  to  denote  a  particular  one.  Sometimes  the 
relative  amount  of  oxygen  is  indicated  by  the  terminations  -ous  and 
-ic ;  in  this  case  -ous  implies  less  oxygen  than  -ic ;  nitrows  oxide 
contains  less  oxygen  than  nitric  oxide.  These  terminations  are  not 


§52.] 


CONDENSATION  OF  NITROGEN  PEROXIDE. 


35 


restricted  in  their  use  to  oxygen  compounds  ;  we  shall,  hereafter, 
meet  such  terms  as  ferrous  chloride  and  ferric  chloride,  stannous  sul- 
phide and  stannic  sulphide. 

52.  Nitrogen  peroxide  (NO2)._ The  red  fumes  of  Exp.  I9b, 
seen  when  nitric  oxide  was  brought  into  the  air,  were  due  to 
the  chemical  union  of  nitric  oxide  with  oxygen  \  a  third  oxide 
of  nitrogen  was  formed, — nitrogen  peroxide.  The  volumetric 
composition  of  nitrogen  peroxide  will  be  understood  from  the 
accompanying  diagram.  The  molecule  will  be  represented  by 
the  formula  NO2,  and  the  composition  of  the  substance  by 
weight  will  be  14  parts  of  nitrogen  and  32  of  oxygen  in  every  46 
parts  by  weight  of  nitrogen  peroxide. 


53.  Although  at  ordinary  temperatures  nitrogen  peroxide  is 
a  gas,  it  can  readily  be  condensed  to  a  liquid.  For  this  purpose, 
it  is  best  prepared  by  heating  a  substance  known  as  lead  nitrate. 

Exp.  20. — Fill  a  perfectly  dry  ignition  tube  about  one-third  full  of 
lead  nitrate  which  has  been  finely  powdered,  and  thoroughly  dried. 
Connect  the  ignition  tube  with  a  dry  bottle,  and  finally  with  the 
water  pan  ;  the  arrangement  is  similar  to  that  in  Fig.  15,  except 
that  the  flask  is  replaced  by  an  ignition  tube.  The  small  bottle 
must  be  surrounded  by  a  mixture  of  ice  (or  snow),  and  salt.  Heat 
the  ignition  tube  gently,  and  when  the  evolution  of  gas  has  once 
begun,  care  must  be  taken  that  the  tube  is  not  suffered  to  cool,  so  as 
to  allow  the  water  to  suck  back  from  the  water  pan.  Red  fumes 
will  fill  the  delivery  tubes,  and  will  condense  in  the  small  bottle  to  a 
brownish-yellow  liquid  if  the  experiment  is  successful.  A  colorless 
gas  will  collect  at  the  water  pan  ;  it  is  oxygen,  as  may  be  shown 
by  the  insertion  of  a  glowing  splinter.  The  chemical  action  may  be 
thus  represented  : — 

PbN206  =  PbO  +  O  +  2NO2. 

Lead  nitrate.      Lead  oxide.  Nitrogen  peroxide. 


36  OXIDES  OF  NITROGEN.  [§  54. 

The  experiment  just  performed  is  interesting,  as  showing  the 
transformation  of  a  substance  which  is  usually  a  gas,  into  a-liquid ; 
in  this  case,  it  was  only  necessary  to  lower  the  temperature.  Many 
other  gases  may  be  liquefied  in  the  same  manner,  by  being  cooled 
to  a  low  temperature;  and  by  the  application  at  the  same  time 
of  a  very  great  pressure,  it  has  been  found  possible  to  liquefy  all 
known  gases,  even  oxygen,  nitrogen  and  hydrogen,  which  until 
recently  were  regarded  as  permanent  or  incondensable  gases. 

54.  Other  Oxides  of  Nitrogen. — A  fourth  oxide  of  nitrogen  is 
an  unstable,  white,  solid  compound  whose  symbol  is  N2O5 .    It  is 
called  nitric  anhydride,  and  is  closely  related  to  nitric  acid. 
Mtric  acid  we  have  already  used,  and  have  learned  that  its  sym- 
bol is  HNO3 .     If  the  oxide  N2O5  be  treated  with  water  the 
action  which  takes  place  may  be  represented  by  the  equation  : — 

H20      +      N205     -     H20,N205     =     2HN03, 

Water.          Nitric  anhydride.  Nitric  acid. 

which  expresses  the  fact  that,  by  the  union  of  one  molecule  of 
water  and  one  molecule  of  nitric  anhydride,  there  are  formed  two 
molecules  of  nitric  acid.  On  account  of  this  reaction,  nitric  acid 
may  be,  and  is  sometimes  regarded  as  a  compound  of  nitric  anhy- 
dride and  water,  and  its  formula  may  be  written,  H2O,  N2O5 . 
The  origin  and  propriety  of  the  term  nitric  anhydride  now 
becomes  apparent ;  for  tjhis  oxide  of  nitrogen,  although  it  is 
obtained  directly  from  nitric  acid  only  with  difficulty,  may  evi- 
dently be  regarded  as  nitric  acid  deprived  of  water  ;  that  is, 
rendered  anhydrous. 

55.  There  is  still  a  fifth  oxide  of  nitrogen  the  symbol  of  which 
is  N2O3 .     This  compound  may  be  formed  as  a  brownish-red  gas, 
similar  to  the  NO2  and  mixed  with  some  of  the  latter  gas,  by 
heating  together  strong  nitric  acid  and  common  starch.     The 
compound  is  called  nitrous  anhydride. 

Exp.  21. — Into  a  flask  of  about  250  c.  c.  capacity,  put  50  c.  c.  of 
strong  nitric  acid,  and  5  grms.  of  starch.  Warm  the  flask  gently  and 
as  soon  as  the  mixture  begins  to  turn  reddish-brown  remove  the  lamp. 
The  experiment  should  be  performed  where  there  is  a  good  draft  of 
air,  as  the  red  fumes  are  copiously  evolved  when  the  action  once  begins. 


§  57.]  LAW  OF  MULTIPLE  PROPORTIONS.  37 

56.  The  oxides  of  nitrogen,  then,  are  — 

Nitrogen  protoxide,  N2O ; 

Nitric  oxide,  NO; 

Nitrous  anhydride,  N2O3  (from  which 

we  have  nitrous  acid,  HNOa); 

Nitrogen  peroxide,  NO2 ; 
Nitric  anhydride,  N2O5  (from  which 

we  have  nitric  acid,  HNO8). 

57.  These  five  bodies   are  all  chemical   compounds;    they 
are  definite  and  constant  in  composition,  and  all  differ  essen- 
tially from  their  elementary  constituents  and  from  each  other, 
as  the  experiments   we  have  performed  with  several  of  them 
have  demonstrated.     It  is,  therefore,   obvious  that  two  of  the 
elements  are  capable  of  combining  in  several   proportions   to 
form  definite  chemical  compounds ;   and  what  is  here  proved 
of  two  of  the  elements  we  shall  hereafter  find  to  be  true  of  all, 
although  not  of  every  couple  :  so  that  the  series  of  oxides  of 
nitrogen  is  but  one  illustration  of  a  most  comprehensive  law. 
The  difference   between  a   mechanical   mixture   and   a   chemi- 
cal compoimd  does  not  on  this  account  become  less  marked. 
The  possible  mixtures  of  nitrogen  with  oxygen  are  innumer- 
able ;    the   known    combinations   of  these   two    elements   are 
only  five :  two  volumes  of  nitrogen  combining  chemically  with 
either  one,   two,   three,   four   or   five  volumes   of  oxygen,  and 
with  no  other  proportions  whatsoever.     As  for  volumes,  so  for 
weights  :  the  proportional  weight  of  oxygen   in   these   oxides 
rises  by  definite  leaps  from  the  first  member  of  the  series  to  the 
last. 

This  definite,  step -by-step  mode  of  forming  chemical  com- 
pounds is  one  of  the  most  characteristic,  as  it  is  one  of  the 
most  general,  facts  of  chemistry;  it  is  the  habitual  mode  in 
which  the  force  called  chemical  ordinarily  acts.  The  abstract 
results  of  observation  and  experiment  may  be  expressed  in  the 
following  proposition,  often  called  the  Law  of  Multiple  Pro- 
portions :  If  two  bodies  combine  in  more  than  one  proper- 


38  AIR  A  MIXTURE.  [§  53. 

tion,  the  ratios  in  which  they  combine  in  the  second,  third  and 
subsequent  compounds,  are  definite  multiples  of  those  in  which 
they  combine  to  form  the  first. 

58.  Air  a  Mixture,  —  The  distinction  between  a  mechani- 
cal mixture  and  a  chemical  combination  may  be  illustrated  by 
the  differences  between  common  air  and  the  oxides  of  nitro- 
gen. Some  of  the  considerations  which  go  to  show  that  air  is 
simply  a  mechanical  mixture  of  oxygen  and  nitrogen  are  as 
follows  :  — 

In  the  first  place,  while  in  the  oxides  of  nitrogen  the  two 
elementary  gases  bear  to  each  other  some  simple  relation  in  re- 
spect to  both  volume  and  weight,  in  air  they  are  mixed  in  the  far 
from  simple  proportion  of  20.81  measures  of  oxygen  to  79.19 
measures  of  nitrogen,  or  23.10  parts  by  weight  of  oxygen  to 
76.90  parts  of  nitrogen;  moreover,  if  20.81  parts  of  oxygen 
are  mixed  with  79.19  of  nitrogen,  there  is  no  development 
of  either  light,  heat  or  electricity,  such  as  usually  attends  the 
formation  of  a  chemical  compound ;  and  the  physical  charac- 
teristics of  the  mixture  are  such  as  should,  according  to  calcu- 
lation, belong  to  a  mere  mixture  of  the  gases. 

Again,  if  nitric  oxide  be  brought  into  contact  with  air,  suffo- 
cating red  fumes  of  nitrogen  peroxide  are  formed ;  but  if  the 
nitric  oxide  be  brought  into  contact  with  nitrogen  protoxide, 
no  fumes  are  produced,  although  this  gas  contains  as  much 
oxygen  as  common  air.  These  experiments  go  to  show  that, 
while  in  nitrogen  protoxide  the  oxygen  is  held  in  chemical  com- 
bination, in  air  it  is  free. 

Further  evidence  that  air  is  a  mere  mixture  is  afforded  by 
its  behavior  towards  water.  All  gases  are  soluble  in  water  to 
a  greater  or  less  extent,  each  one  dissolving  in  a  certain  fixed 
and  definite  proportion  at  any  given  temperature.  If  pure 
water  be  exposed  to  nitrogen  protoxide,  it  will  dissolve  a  certain 
amount  of  that  gas,  which  may  be  recovered  unchanged  by 
boiling  the  water.  When  water  which  has  been  exposed  to 
the  air  is  boiled,  a  gaseous  mixture  containing  oxygen  and  ni- 
trogen is  given  off  (Exp,  10,  §  33) ;  but  it  has  been  found  that 


59.] 


NITRIC  ACID. 


the  gases  are  mixed  in  a  different  proportion  from  that  in  which 
they  exist  in  the  atmosphere.  The  water,  in  fact,  dissolves  out 
from  the  air  a  quantity  of  oxygen,  just  as  if  no  nitrogen  were 
present;  at  the  same  time  it  dissolves  nitrogen  to  precisely 
the  same  extent  that  it  would  dissolve  that  gas  if  there  were 
110  oxygen  in  the  air. 

59.  Nitric  Acid  (HNO3).  —  In  the  preparation  of  the  various 
oxides  of  nitrogen  we  have  used  either  nitric  acid  or  a  compound 
which  we  have  designated  as  a  nitrate,  as,  for  example,  ammonium 
nitrate  in  Exp.  17,  and  lead  nitrate  in  Exp.  20.  We  now  pro- 
ceed to  a  study  of  those  compounds,  and,  in  the  first  place,  of 
nitric  acid  itself.  Two  abundant  sources  of  this  material  are 
found  in  nature  and  are  familiar  as  articles  of  commerce.  Salt- 
petre or  nitre,  a  whitish  saline  crystallized  substance,  now  mainly 
brought  from  India,  is  one  of  these  sources  ;  a  similar  substance, 
known  in  commerce  as  "  nitrate  of  soda,"  is  collected  on  a  desert 
tract  in  Chili  and  Peru,  and  forms  a  valuable  article  of  export 
from  those  countries.  These  two  substances  differ  from  each 
other  only  in  this,  —  that  the  first  contains  potassium,  the  second 
the  very  similar  element  sodium,  in  either  case  combined  with 
definite  proportions  of  the  elements  nitrogen  and  oxygen.  By 
the  reaction  of  sulphuric  acid  (oil  of  vitriol)  on  either  of  these 
two  substances,  nitric  acid  is  obtained. 

Exp.  22.  —  Into  a  tubftlated  glass-stoppered  retort  of  250  c.  c. 
capacity,  put  40  grammes  of  powdered  potassium  nitrate,  or,  better, 
34  grammes  of  powdered  sodium  nitrate,  if  it  can  be  obtained,  and 
through  the  tubulure  pour  50  grammes  of  strong  sulphuric  acid, 
which  has  been  weighed  out  in  a  bottle  previously  counterpoised 
upon  the  balance  with  shot  or  coarse  sand.  Imbed  the  bottom  of  the 
retort  in  sand  contained  in  a  small  iron  pan  placed  over  the  gas-lamp 
on  a  ring  of  the  iron  stand.  Thrust  the  neck  of  the  retort  into  a  re- 
ceiver with  two  tubulures  ;  the  retort-neck  should  fit  the  tubulure 
of  the  receiver  with  tolerable  accuracy.  The  second  tubulure  of  the 
receiver  should  be  left  open,  or  loosely  covered  with  a  bit  of  glass,  in 
order  to  avoid  the  possibility  of  any  pressure  being  created  within  the 
retort  during  the  operation.  Place  the  receiver  in  a  pan  of  cold  water, 
and  cover  it  with  cloth  or  bibulous  paper,  which  must  be  kept 


NITRIC  ACID. 


[§60. 


i1*4  wet  during  the  distillation.     (See  Fig. 

17.)  Heat  the  sand-bath  moderately 
(that  the  frothing  which  occurs  may 
not  become  too  violent) ;  reddish  vapors 
appear  for  a  moment,  then  disappear, 
and  a  yellowish  fuming  liquid  begins 
to  condense  in  the  neck  of  the  retort 
and  to  run  down  into  the  receiver. 
When  all  frothing  has  ceased  and  the 
mass  in  the  retort  is  in  a  state  of  tran- 
quil fusion,  while  very  little  liquid 
passes  over  into  the  receiver,  the  lamp  is  to  be  put  out. 

The  very  acid,  corrosive  and  poisonous  liquid  in  the  receiver  is 
nitric  acid  ;  its  faint  color  is  not  its  own,  but  is  due  to  the  presence 
of  a  compound  of  nitrogen  and  oxygen  already  described  (NO2). 
Transfer  the  liquid  to  a  glass-stoppered  bottle,  and  keep  it  for  future 
use.  In  all  manipulations  with  nitric  acid,  it  is  desirable  to  avoid 
getting  it  upon  the  skin,  since  it  produces  rather  permanent  yellow 
stains. 

As  the  retort  cools,  the  residue  solidifies  into  a  white,  saline  mass, 
which  must  be  dissolved  out  of  the  vessel  by  heating  it  with  water 
after  the  apparatus  has  become  thoroughly  cold.  It  will  be  observed 
that  the  liquid  sulphuric  acid  which  was  used  has  disappeared,  al- 
though the  saline  residue  is  still  intensely  acid. 

60.  Nitric  Acid  is  much  used  in  the  arts,  and  is  prepared 
on  the  large  scale  from  the  same  materials  as  here  employed. 
The  retorts  are  huge  iron  cylinders  or*  kettles  and  the  acid  is 
collected  in  stoneware  bottles.  The  pure  acid  is  colorless  and  is 
about  half  as  heavy  again  as  water.  It  may  be  mixed  with  water 
in  all  proportions. 

Exp.  23. — To  about  1  c.  c.  of  the  nitric  acid  obtained  in  the  last 
experiment  add  10  times  its  bulk  of  water.  Notice  the  sour  taste  by 
touching  a  drop  of  this  diluted  acid  to  the  tip  of  the  tongue.  Into 
the  solution  thrust  a  strip  of  litmus  paper ;  it  will  be  turned  red, 
showing  that  in  spite  of  the  amount  of  water  added,  the  liquid  is  still 
strongly  acid.  Litmus  is  a  blue  coloring  matter,  prepared  from  various 
lichens.  Unsized  paper,  colored  with  a  solution  of  litmus  in  water, 
is  a  convenient  test  for  many  acids,  which,  as  a  rule,  change  the  color 
of  the  paper  from  blue  to  red. 


§  61.]  ACIDS,   BASES  AND  SALTS.  4l 

61.  Acids,  Bases  and  Salts. — Citric  acid  is  an  example  of 
the  class  of  bodies  to  which"  the  term  acid  is  generally  applied. 
There  is  a  class  of  bodies  which  act  upon  vegetable  colors  in  just 
the  opposite  way  from  the  acids,  and  will  in  fact  neutralize  their 
action  in  many  cases.  As  an  example  of  these  substances,  which 
are  generally  spoken  of  as  bases,  and  which  when  soluble  in 
water  have  what  is  called  an  alkaline  reaction,  we  may  take 
caustic  potash. 

Exp.  24. — Dissolve  about  one  gramme  of  caustic  potash  in.  20  c.  c. 
of  water.  Notice  the  character  of  the  solution  by  rubbing  a  little 
between  the  fingers,  and  by  touching  a  small  drop  to  the  tip  of  the 
tongue.  Into  the  liquid  thrust  the  litmus  paper,  which  was  reddened 
by  the  nitric  acid  in  Exp.  23.  It  will  be  turned  blue. 

The  terms  acid  and  base  which  we  have  used  cannot  be  defined 
with  exactness,  because  they  are  not  applied  by  chemists  with 
uniform  precision  to  well-detined  classes  of  substances.  We  may 
say,  however,  in  general  terms,  that  the  acids  commonly  possess 
a  sour  taste  and  act  in  a  peculiar  way  upon  vegetable  colors  (as 
nitric  acid  reddened  the  litmus  paper  in  Exp.  22).  The  acids 
are  usually  compounds  of  hydrogen,  oxygen  and  some  one  other 
chemical  element,  as,  for  example,  nitric  acid  (HNO3)  •  bases, 
likewise,  are  compounds  of  hydrogen,  oxygen  and  some  one  other 
chemical  element,  as,  for  example,  caustic  potash  (KHO) ;  but 
while  certain  elements  in  uniting  with  hydrogen  and  oxygen  form 
by  preference  acids,  other  elements  form  by  preference  bases. 
The  so-called  non-metallic  elements,  such  as  nitrogen,  sulphur, 
etc.,  generally  form  acids:  for  example,  nitric  acid  (HNO3)  and 
sulphuric  acid  (H2SO4).  The  metallic  elements,  such  as  potas- 
sium, sodium,  copper,  etc.,  form  bases ;  thus  caustic  potash  or 
potassium  hydrate  (KHO),  sodium  hydrate  (NaHO)  and  copper 
hydrate  (CuH2O8),  are  bases. 

An  important  characteristic  of  the  acids  and  bases  is  that  they 
have  the  power,  when  one  of  either  class  is  brought  into  contact 
with  one  of  the  other  and  opposite  class,  of  forming  new  com- 
pounds possessing  the  characters  of  neither  the  acid  or  base  from 
which  the  new  compound,  or  salt  as  it  is  called  has  been  formed. 


42  ACIDS,  BASES  AND  SALTS.  [§  62. 

62.  The  relations  between  acids  and  bases  may  be  illustrated 
by  the  following  experiment  :  — 

Exp.  25.  —  To  one-third  of  the  nitric  acid  of  Exp.  22,  §  59,  diluted 
with  twice  its  bulk  of  water,  add  cautiously  a  rather  dilute  solution 
of  caustic  potash  (potassium  hydrate,  KHO)  until  the  mixture  turns 
litmus-paper  neither  red  nor  blue.  Evaporate  the  solution  in  a  por- 
celain dish,  taking  care  that  the  liquid  does  not  actually  boil,  until  a 
drop  taken  out  on  the  end  of  a  glass  rod  becomes  nearly  solid  on 
cooling.  Then  remove  the  lamp,  and  allow  the  dish  to  become  cold. 
The  crystals  which  will  separate  from  the  liquid  are  potassium  ni- 
trate, a  compound  which  has  already  been  used  in  the  manufacture  of 
nitric  acid.  The  change  that  has  taken  place  may  be  thus  sym- 
bolized :  — 


+       KHO       =       KN03       +       H2O. 

Nitric  acid.  Caustic  potash.  Potassium  nitrate.  Water. 

The  water  in  which  the  nitric  acid  and  caustic  potash  were  dis- 
solved, together  with  that  set  free  by  the  reaction,  has  for  the  most 
part  been  removed  by  evaporation.  It  might  have  been  removed 
entirely  if  the  evaporation  had  been  carried  further.  The  potassium 
nitrate  would  then  be  obtained  as  a  white  crystalline  substance,  but 
not  in  well-defined  crystals. 

When,  as  in  the  above  experiment,  an  acid  and  a  base  are 
brought  into  contact,  there  is  formed,  besides  water,  a  new  com- 
pound. This  compound  is  called  a  salt,  the  name  being  applied 
to  it  on  account  of  the  general  resemblance  which  this  class  of 
compounds  bear  to  common  salt,  —  one  of  the  earliest  known 
and  most  familiar  of  saline  bodies. 

63.  If  we  compare  the  formula  of  nitric  acid  (HNO3)  with 
that  of  potassium  nitrate  (KNO3),  we  shall  observe  a  striking 
resemblance  between  the  two  ;  the  two  formulas  are  in  fact 
identical,  except  that  in  the  one  case  we  have  K>  the  symbol  for 
potassium,  where  in  the  other  we  have  H>  the  symbol  for  hydro- 
gen. Potassium  nitrate  is  only  one  of  a  class  of  analogous  com- 
pounds called  nitrates  ;  the  formula  of  each  member  of  the  class 
is  that  of  one  or  more  molecules  of  nitric  acid,  (HNO3  ,  H2N2O6, 
etc.,)  except  that  the  hydrogen  is  replaced  by  some  metallic 


§  63.]  ACIDS,  BASES  AND  SALTS.  43 

element.  We  have,  indeed,  already  used  several  of  these  nitrates. 
Thus  in  Exp.  20,  we  used  lead  nitrate,  the  symbol  of  which  is 
PbN2O6>  and  in  Exp.  19,  we  prepared  copper  nitrate  which  re- 
mained in  the  solution,  and  the  symbol  of  which  is  CuN2O6. 

As  the  nitrates  correspond  to  nitric  acid,  so  corresponding  to 
every  acid,  there  is  a  series  of  salts,  the  name  common  to  all  the 
series  being  derived  from,  the  name  of  the  acid.  Thus  corres- 
ponding to  sulphuric  acid  there  are  numerous  sulphates,  corres- 
ponding to  phosphoric  acid  there  are  phosphates,  to  oxalic  acid 
oxalates,  etc.  As  will  be  noticed  in  the  cases  above  mentioned, 
the  acid  is  designated  by  a  term  ending  in  ic}  and  the  term  ap- 
plied to  the  salts  ends  in  ate  ;  if,  however,  the  name  given  to  the 
acid  ends  in  ous,  the  name  given  to  the  salts  ends  in  ite  ;  thus, 
corresponding  to  nitrous  acid  we  have  a  series  of  nitrites  ;  thus, 
nitrous  acid,  HNO2  f  potassium  nitrite,  KNO2 . 

Further  use  of  the  terms  Acid  and  Base. — The  term  acid, 
besides  being  used  as  denned  in  §  61,  is  applied  to  certain  bodies 
which  are  destitute  of  oxygen,  like  chlorhydric  acid  (HCl)  •  These 
acids  are  those  formed  by  the  union  of  hydrogen  with  some  mem- 
ber of  the  chlorine  group  (see  page  65),  and  a  few  others.  The 
salts  corresponding  to  such  acids  are  designated  by  terms  ending 
in  ide  ;  thus  we  have  chlorides,  bromides  and  fluorides  from 
chlorhydric,  bromhydric  and  fluorhydric  acids  respectively. 

The  term  base  is  sometimes  used  to  denote  certain  compounds 
which  contain  no  hydrogen.  If  potassium  oxide  (K2O),  which 
may  be  formed  by  heating  metallic  potassium  in  dry  air  or  oxy- 
gen gas,  be  treated  with  nitric  acid,  the  following  reaction  will 
take  place  : — 

K20  +  2  HN03  =  2  KNO ,  +  H2O. 

The  same  "salt,"  potassium  nitrate  (KNO3),  is  produced  as  in 
Exp.  25,  where  potassium  hydrate  and  nitric  acid  were  brought 
together.'  On  account  of  their  taking  part  in  such  reactions  as 
these,  the  anhydrous  oxides  of  the  metallic  elements  are  often 
spoken  of  as  bases.  In  some  cases  the  oxide  is  more  commonly 
employed  than  the  hydrate,  or  base  proper,  in  neutralizing  acids 
and  in  forming  salts.  This  is  the  case  with  oxide  of  lead. 


44 


NITROGEN  AND  HYDROGEN. 


[§64 


Exp.  26. — Put  the  nitric  acid  which  remains  from  Exp.  21,  into 
an  evaporating  dish,  dilute  with  twice  its  bulk  of  water,  and  add 
finely  powdered  litharge  as  long  as  it  readily  dissolves.  Evaporate 
the  solution  carefully  to  dryness,  using  a  very  gentle  heat.  There 
remains  a  white  saline  substance  which  is  lead  nitrate  such  as  was 
used  in  Exp.  20.  Its  formation  is  thus  represented  : — 
PbO  +  2HN03  =  Pb!NV06  +  H2O. 

Lead  oxide.  Lead  nitrate. 

The  term  anhydride  (or  more  definitely,  acid  anhydride)  is 
commonly  applied  to  an  oxide  of  a  non-metallic  element,  which 
in  combination  with  the  elements  of  water  forms  an  acid,  as  was 
illustrated  by  nitric  anhydride  in  §  54.  To  these  anhydrides 
the  term  acid  was  formerly  applied,  as  well  as  to  ijie  acids  proper. 
To  distinguish  between  the  two  sorts  of  compounds,  the  terms 
anhydrous  and  hydrated  were  employed ;  thus,  N.,O5  was  known 
as  anhydrous  nitric  acid,  and  HNO3  as  hydrated  nitric  acid. 

NITROGEN    AND    HYDROGEN. 

64.  Nitrogen  and  Hydrogen. — While  there  are  five  com- 
pounds of  nitrogen  with  oxygen,  there  is  but  one  known  com- 
pound of  nitrogen  and  hydrogen.  This  is  a  gas,  and  may  be 
readily  prepared  from  ammonia-water, — the  aqua  ammonice  of 
the  druggists. 

Fill  a  flask  of  250  to 
500  c.  c.  capacity  about 
half  full  of  the  strongest 
ammonia-water  to  be 
had  at  the  druggist's. 
Close  the  flask  by  a  cork 
provided  with  a  funnel- 
tube  and  an  exit-tube  ; 
carry  the  delivery-tube 
to  the  bottom .  of  a  tall 
bottle,  having  a  capaci- 
ty of  at  least  a  litre,  and 
filled  with  fragments  of 
quick-lime.  When  the 
ammonia-water  in  the 


Fig    18. 


§  65.]  PROPERTIES  OF  AMMONIA.  45 

flask  is  gently  boiled,  the  gas  which  passes  off  will  be  deprived  of 
moisture  by  the  quick-lime,  arid  will  issue,  dry  from  the  bottle  ;  it  may 
be  collected  over  mercury,  or  by  displacement,  as  shown  in  the  figure 
(Fig.  18).  The  gas  is  so  extremely  soluble  in  water,  that  it  cannot  be 
collected  over  the  ordinary  water-pan  ;  as  it  has  little  more  than  half 
the  density  of  atmospheric  air,  it  can  be  readily  collected  by  displace- 
ment. When  thus  collected,  the  gas  should  be  allowed  to  pass  into 
the  very  loosely  corked  bottle,  until  a  piece  of  turmeric  paper,  held  at 
the  mouth,  is  immediately  turned  brown  ;  the  delivery-tube  is  then 
withdrawn,  and  the  mouth  of  the  bottle  is  tightly  closed  with  a 
caoutchouc  or  glass  stopper. 

If  the  gas  be  collected  over  mercury,  the  flask  must  be  provided 
with  a  very  long  funnel-tube  ;  for  the  pressure  to  be  overcome  by  the 
gas  in  forcing  its  way  through  even  a  few  centimetres  of  mercury  is 
quite  considerable,  and  unless  the  funnel-tube  were  long  enough  to 
sustain  a  column  of  liquid  exerting  an  equal  pressure,  the  liquid  in 
the  flask  would  be  forced  out  through  this  tube. 

The  gas  thus  obtained  is  transparent  and  colorless,  possesses 
an  extraordinarily  pungent  odor  which  provokes  tears,  and  has  an 
acrid,  alkaline  taste.  It  will  be  found  to  be  uninflammable,  and 
is,  of  course,  irrespirable.  It  turns  red  litmus  to  blue  most  ener- 
getically. One  measure  of  water  at  0°  dissolves  1,049  measures 
of  the  gas. 

The  ready  solubility  of  ammonia-gas  may  be  illustrated  as  fol- 
lows :  Fill  a  stout  glass  tube  —  an  ignition -tube,  for  example,  —  over 
mercury  with  the  gas  ;  grasp  the  tube  by  the  top,  and,  holding  it  up- 
right, dip  its  mouth  into  a  vessel  of  water.  The  water  will  rush  up 
the  tube,  if  the  gas  be  pure,  with  a  force  which  might  break  the  tube, 
if  too  thin. 

65.  The  solution  of  ammonia  if  exposed  to  the  air,  or  placed 
in  a  vacuum,  or  simply  boiled,  loses  all  its  gas.  When  the  gas 
is  cooled  to  0°  and  subjected  to  a  pressure  of  4£  atmospheres,  it 
is  converted  into  a  transparent  mobile  liquid.  The  gas  may 
also  be  liquefied  at  the  ordinary  pressure  if  cooled  to  — 40°. 
Liquid  ammonia  in  passing  into  the  gaseous  state  absorbs  a  large 
amount  of  heat  from,  surrounding  objects.  In  certain  machines 
for  the  production  of  ice  artificially,  advantage  is  taken  of  this 


46 


AMMONIUM  SALTS. 


[§66. 


fact,  the  necessary  cooling  of  the  water  being  produced  by  the 
rapid  evaporation  of  liquefied  ammonia-gas,  in  contact  with  the 
vessel  containing  the  water. 

66.  Analysis  of  dry  ammonia-gas  has  shown  that  it  is  made 
up  of  nitrogen  and  hydrogen  in  the  proportion  of  one  volume 
of  nitrogen  to  three  volumes  of  hydrogen,  the  four  volumes  of 
the  elementary  gases  being  condensed  to  two  volumes  in  the 
compound.  The  formula  of  its  molecule  is  NH3,  and  its  com- 
position may  be  represented  by  the  diagram,  — 


H 

1 


67.  Ammonium  Salts, — Since  ammonia-water  gives  off  the 
gas  so  easily  when  boiled  or  even  when  exposed  to  the  air,  it  might 
seem,  at  first  sight,  that  it  was  a  case  of  simple  physical  solution ; 
there  is,  however,  good  reason  for  considering  that  each  molecule 
of  ammonia  is  in  combination  with  a  molecule  of  water,  in  the 
form  of  the  compound  NH3)  H2O  or  NH.O.  This  compound  may 
be  supposed  to  be  dissolved  in  the  water  present  in  excess  of 
what  is  necessary  to  form  the  compound.  When  ammonia-water 
is  mixed  with  nitric  acid,  a  reaction  occurs  like  that  which  takes 
place  when  nitric  acid  is  mixed  with  a  solution  of  caustic 
potash  (Exp.  25,  §  62) ;  there  is  formed  a  salt  called  ammo- 
nium nitrate,  resembling  potassium  nitrate  ;  but,  in  order  to 
bring  out  the  resemblance,  the  elements  of  the  compound  of 
ammonia  and  water  must  be  so  arranged  as  to  exhibit  its  analogy 
with  caustic  potash,  whose  formula  is  KHO-  For  that  purpose, 
its  formula  must  be  written  (NH4)HO,  so  that  the  group  of 
elements  NH4  shall  stand  in  the  formula  of  ammonia-water 
where  the  element  potassium  stands  in  the  formula  of  caustic 


§  68.1  SOURCES  OF  AMMONIA  47 

potash.     The  reaction  between  ammonia-water  and  nitric  acid 
may  then  be  represented  by  the  equation,  — 

(NHJHO      .+       HN03  (NH4)N03       +        H2O, 

Ammonia-water.  Nitric  acid.  Ammonium  nitrate.  Water. 

just  like  — 

KHO   -f  HN03    ==    KN03    -f   H2O. 

If  now  the  formula  of  ammonium  nitrate,  (NH4)NO8)  be 
compared  with  that  of  nitric  acid,  HNO3,  it  will  appear  that 
the  group  of  atoms  NH4  replaces  the  atom  H,  just  as  the  atom 
K  did  in  the  formula  of  potassium  nitrate  :  for  this  reason  it 
has  been  found  convenient  to  give  to  this  group  of  atoms  a  name 
bearing  some  resemblance  to  the  names  of  metals  ;  and  it  has, 
therefore,  been  called  ammonium.  Ammonium  is  known  only 
in  its  compounds ;  many  attempts  have  been  made  to  obtain  it 
in  .a  free  state,  but  hitherto  in  vain  :  as  soon  as  the  group  of 
atoms  escapes  from  combination,  it  is  resolved  into  ammonia  and 
hydrogen.  The  important  compounds  into  which  ammonium 
enters,  commonly  called  the  salts  of  ammonium,  will  be  studied 
hereafter  in  immediate  connection  with  the  analogous  salts  of 
sodium  and  potassium. 

68.  Ammonia  exists  in  very  minute  quantity  in  the  atmos- 
phere, and  hence  in  rain-water,  fog  and  dew.  It  is  given  off 
by  putrefying  animal  and  vegetable  substances  containing  nitro- 
gen, and  almost  every  process  of  slow  oxidation  in  the  presence 
of  air  and  moisture  is  attended  with  the  formation  of  ammonia 
or  ammonium  salts.  The  chief  source,  however,  of  ammonium 
compounds  is  the  decomposition,  either  by  putrefaction  or  by 
destructive  distillation,  of  nitrogenous  organic  matter.  The  dis- 
tillation of  bones  and  animal  refuse,  for  the  purpose  of  making 
bone-black,  yields  a  large  amount  of  ammoniacal  liquor,  which 
was  formerly  the  principal  source  of  ammonium  compounds. 
The  horns  of  deer  used  to  be  thus  distilled ;  whence  the  name 
"  hartshorn."  At  present,  the  destructive  distillation  of  coal  in 
gas-works  furnishes  the  great  bulk  of  ammonium  compounds 
used  in  the  arts. 


48  MAKING  AMMONIA-WATER.  [§  69. 

69.  The  solution  of  ammonia-gas  in  water  is  a  reagent  con- 
tinually required,  as  a  test,  in  the  laboratory,  and  much  used 
in  the  arts.  The  solution  is  colorless,  intensely  alkaline,  has 
a  caustic  taste,  and,  when  concentrated,  blisters  the  skin  ;  it 
is  lighter  than  water,  and  so  much  the  lighter  in  proportion  to 
the  amount  of  ammonia  that  it  contains.  The  solution  may 
be  prepared  from  a  mixture  of  ammonium  chloride  and  slaked 
lime. 

Exp.  27.  —  Mix   25  grms.    of  ammonium   chloride,   a   substance 
generally  sold  under  the  name  of  sal  ammoniac,  with  about  the  same 
19.  weight    of    cold,    freshly-slaked 

lime.  Introduce  the  mixture 
into  a  flask  of  500  c.  c.  capacity, 
and  place  the  flask  on  a  sand- 
bath  over  the  gas-lamp.  Close 
the  mouth  of  the  flask  with  a 
good  cork,  provided  with  a  de- 
livery-tube so  bent  as  to  con- 
nect conveniently,  by  means  of 
a  caoutchouc  connector,  with  the 
first  of  the  series  of  three-necked 
bottles  (Woulfe-bottles)  represented  in  Fig.  19.  On  heating  the  mix- 
ture, ammonia-gas  will  be  disengaged,  and  will  be  absorbed  by  the 
water  in  the  Woulfe-bottles. 

The  first  of  this  series  of  bottles  is  smaller  than  the  rest,  and  is  not 
filled  so  full  of  water  as  the  others  ;  it  should  be  kept  cool  by  immer- 
sion in  cold  water  ;  the  delivery -tube  coming  from  the  flask  into  this 
bottle  must  not  dip  into  the  water  at  all,  so  that  it  will  be  impossible 
for  any  water  to  suck  back  into  the  flask,  should  the  gas  suddenly 
cease  to  come  off  from  the  dry  mixture.  The  construction  of  the 
apparatus  will  be  easily  understood  from  the  figure  ;  the  open  tube 
which  dips  beneath  the  water  in  each  bottle  is  a  safety-tube,  which 
by  admitting  air  into  any  bottle  in  which  a  partial  vacuum  may  hap- 
pen to  be  created  by  rapid  absorption,  prevents  the  contents  of  the 
succeeding  bottle  from  flowing  back  into  it.  In  order  to  show  the  action 
of  the  safety-tubes,  the  open  tube  in  the  first  bottle  may  be  closed  for 
a  moment  with  the  finger,  and  the  bottle  shaken  very  gently.  Water 
will  be  immediately  forced  back  from  the  second  bottle  through  the 
connecting-tube  to  fill  the  vacuum  caused  by  the  absorption  of  the 


§  70.]  CHLORHYDRIC  ACID.  49 

ammonia-gas  ;  but  the  moment  the  finger  is  removed  from  the  safety- 
tube,  air  will  enter  through  the  latter  to  fill  the  vacuum,  and  the 
water  in  the  connecting-tube  will  fall  back  into  the  second  bottle. 
The  ammonia-gas  can  not  avoid  three  separate  contacts  with  water  as 
it  passes  through  the  apparatus,  so  that  all  the  gas  is  sure  to  be  ab- 
sorbed ;  the  contents  of  the  first  bottle  will  not  be  as  pure  as  those  of 
the  succeeding.  In  this  experiment  the  gas  will  be  mostly  absorbed 
in  the  first  and  second  Woulfe-bottles. 

The  reaction  between  the  ammonium  chloride  and  the  slaked 
lime  is  represented  by  the  following  equation  :  — 

2NH.C1     -f     CaH202        j    2NH3     -f-     CaCl2     -f    2H2O. 

Ammonium  chloride.    Slaked  lime.  Ammonia.     Calcium  chloride.        Water. 

Ammonium  chloride  is  a  compound  which  may  be  obtained  by 
bringing  together  dry  ammonia,  NH3,  and  dry  muriatic-acid 
gas,  HC1. 

NH3  -f-  HC1  =  NH4CL 

It  may  obviously  be  regarded  as  a  compound  of  the  group  called 
ammonium,  NH4 ,  with  the  element  chlorine  ;  from  this  view  is 
derived  the  name  ammonium  chloride.  Slaked  lime  is  prepared 
by  adding  water  to  quick-lime,  which  is  chemically  the  oxide  of 
the  metal  calcium, 

CaO  +  H20  =  CaH,Or 


CHAPTER  VII. 
CHLORHYDRIC  ACID, 

70.  Muriatic  (sea-salt)  acid,  called  in  modern  nomenclature 
chlorhydric  acid,  is  a  liquid  which  has  been  known  for  centu- 
ries, and  is  to-day  an  article  of  commerce,  largely  employed  in 
the  useful  arts.  The  pure  acid  is  a  gas,  as  ammonia  is  ;  the 
liquid  muriatic  acid  of  commerce  is  only  an  aqueous  solution  of 
5 


50 


CHLORHYDRIC  ACID. 


[§n. 


Fig.  30. 


this  gas,  and  gives  it  up  when  heated,  precisely  as  ammonia- 
water  yields  ammonia-gas. 

This  operation  may  be  conveniently  performed  in  the  apparatus 

shown  in  Fig.  20.  About 
250  c.  c.  of  the  commer- 
cial acid  is  poured  in- 
to the  flask,  which  is 
then  moderately  heated: 
the  gas  disengaged  is 
charged  with  aqueous 
vapor,  which  needs  to 
be  removed  before  the 
gas  is  collected.  For 
this  purpose  the  deliv- 
ery-tube is  carried  to  the 
bottom  of  a  bottle  filled 
with  pieces  of  pumice- 
stone  saturated  with 
strong  sulphuric  acid  :  the  moisture  of  the  gas  is  greedily  absorbed  by 
the  large  surface  of  acid  with  which  the  gas  comes  into  contact,  as  it 
is  forced  upward  through  the  acid-soaked  stone.  The  dry,  colorless, 
transparent  gas  must  be  collected  over  mercury,  for  it  is  extremely 
soluble  in  water. 

The  gas  is  strongly  acid  in  taste  and  reaction  on  vegetable 
colors,  provokes  violent  coughing  and  is  wholly  irrespirable.  It 
is  neither  combustible,  nor  will  it  support  combustion.  The  gas  is 
somewhat  heavier  than  air  :  it  is  very  soluble  in  water,  and  may 
be  condensed  to  a  liquid,  although  with  difficulty. 

The  avidity  of  water  for  chlorhydric  acid  gas  may  be  neatly  shown 
by  thrusting  a  bit  of  ice  into  a  small  cylinder  of  the  dry  gas  standing 
over  mercury  :  the  ice  instantly  melts,  and  the  gas  as  quickly  disap- 
pears. 

71.  The  composition  of  the  gas  has  been  determined,  both  by 
analysis  and  by  synthesis  ;  and  it  has  been  found  that  one 
volume  of  hydrogen  is  combined  with  one  volume  of  the  ele- 
mentary gas  chlorine  (Cl)  to  form  two  volumes  of  chlorhydric 
acid.  The  molecule  of  chlorhydric  acid  will  be  represented  by 
the  formula  HC1 ;  and,  as  the  specific  gravity  of  chlorine,  that 


72.] 


CHLORHYDRIC  ACID. 


51 


is,  the  weight  of  any  volume  compared  with  an  equal  volume 
of  hydrogen,  is  35.5,  the  following  diagram  represents  the  com- 
position of  this  important  compound,  both  by  volume  and  by 
weight  :  — 


.  72.  The  muriatic  acid  of  commerce  is  made  from  the  most 
abundant  and  cheapest  of  all  the  natural  compounds  of 
chlorine,  —  common  salt,  whose  chemical  name  is  sodium 
chloride,  and  whose  formula  is  NaCl.  This  substance  sup- 
plies the  chlorine  :  the  necessary  hydrogen  is  obtained  from 
common  sulphuric  acid  (oil  of  vitriol),  whose  composition, 
as  expressed  in  its  formula  H2SO4,  we  have  already  become 
familiar  with.  The  reaction  is  somewhat  various,  according  to 
the  proportion  of  sulphuric  acid  employed  j  it  may  be  either  of 
the  reactions  expressed  in  the  following  equations  :  — 


NaCl          -f        H2SO4 

Sodium  chloride.  Sulphuric  acid. 

2  NaCl        -f         H2S04 


HC1         -}-        HNaSO4; 

Chlorhydric  Hydrogen  Sodium 

sulphate. 


acid. 


2  HC1 


-f         Na2SO4. 

Sodium  sulphate. 


In  the  first  of  these  reactions,  only  one-half  of  the  hydrogen  in 
each  molecule  of  sulphuric  acid  is  replaced  by  sodium  ;  in  the  second, 
both  atoms  of  hydrogen  are  thus  replaced.  The  first  reaction  requires 
more  sulphuric  acid,  in  proportion  to  the  amount  of  the  product  than 
the  second,  but  is  accomplished  with  less  wear  of  the  apparatus,  be- 
cause a  more  moderate  heat  suffices  for  the  first  than  for  the  second 
reaction. 

On  the  manufacturing  scale,  the  salt  and  sulphuric  acid  are  heated 
in  large  iron  cylinders,  and  the  evolved  gas  is  absorbed  by  water  con- 
tained in  a  series  of  stoneware  Woulfe-bottles.  The  ordinary  com- 
mercial acid  contains  from  30  to  40  per  cent  by  weight  of  real  acid. 

Exp.  28. — Place  30  grms.  of  dry  (or  better,  fused)  coarsely  powdered 


52 


PREPARATION  OF  CHLORHYDRIC  ACID. 


[§73. 


salt,  in  a  flask  of  a  litre  capacity,  provided  with  a  delivery-tube  which 
can  be  conveniently  connected  by  a  caoutchouc  connector  with,  a 
'  ,.  21.  series  of  small  Woulfe-bottles, 

such  as  is  represented  in  Fig.  21. 
Pour  50  grms.  of  strong  sul- 
phuric acid  upon  the  salt,  and 
immediately  cork  the  flask,  place 
it  upon  a  sand-bath  on  the  iron- 
stand  and  connect  the  delivery- 
tube  with  the  Woulfe-bottles. 
The  tubes  by  which  the  gas  en- 
ters the  bottles  should  barely  dip 
beneath  the  water  contained  in 
them,  inasmuch  as  the  solution  of  chlorhydric  acid  is  heavier  than 
water  :  the  bottles  should  not  be  more  than  half  full,  for  the  water 
becomes  hot,  and  increases  considerably  in  bulk.  As  hot  water  holds 
less  gas  in  solution  than  cold  water,  it  is  not  amiss  to  place  each  three- 
necked  bottle  in  a  vessel  of  cold  water.  The  first  Woulfe-bottle  should 
contain  but  a  small  quantity  of  water,  and  the  tube  coming  from  the 
flask  should  not  dip  into  this  water.  The  contents  of  the  flask  must 
be  very  gradually  and  moderately  heated,  else  a  violent  frothing  is 
liable  to  occur,  which  would  spoil  the  experiment.  The  acid  will  be 
purer  in  the  second  bottle  than  in  the  first,  in  the  third  than  in  the 
second,  and  so  forth. 

73.  The  uses  of  chlorhydric  acid  are  very  numerous  :  it  ia 
employed  in  making  chlorine,  potassium  chlorate,  and  "  chloride 
of  lime  "  (bleaching  powder) ;  in  preparing  ammonium  chloride 
and  tin  chloride  ;  in  the  manufacture  of  gelatin ;  for  dissolving 
metals,  either  by  itself  or  mixed  with  nitric  acid  ;  and  it  is  one 
of  the  most  useful  reagents  in  the  chemical  laboratory. 

74.  Chlorhydric  acid,  as  has  already  been  stated  (§  63),  differs 
from  the  other  acids  with  which  we  have  become  acquainted  in  that 
it  contains  no  oxygen. 

As  there  are  certain  compounds  called  nitrates  whose  formulae 
may  be  derived  from  that  of  nitric  acid  by  replacing  the  symbol  of 
hydrogen  in  the  acid  by  that  of  some  metallic  element  ;  so  there  is  a 
series  of  compounds,  the  formula  of  which  may  be  derived  from  that 
of  chlorhydric  acid  by  putting  the  symbol  of  a  metallic  element  in 
the  place  of  the  symbol  of  hydrogen  in  the  acid.  These  compounds 


fc  75  I  QUANT1VALENCE.  53 

o  *  J 

are  called  chlorides :  thus  sodium  chloride,  common  salt,  is  NaCl. 
Chlorides  are  formed  in  some  cases  by  treating  the  metal  with  chlor- 
hydric  acid,  as  in  the  formation  of  zinc  chloride  (ZnCl2),  Exp.  11, 
§  35  :  in  other  cases  they  are  formed  by  treating  the  oxide,  or  the 
hydrate,  of  the  metal  with  chlorhydric  acid,  as  may  be  seen  in  these 
equations  :  — 

NaHO         -f         HC1         =         NaCl         +         H2O ; 

Sodium  hydrate.  Sodium  chloride. 

Ag20  -f     2HC1        =     2AgCl         +        H20; 

Silver  oxide.  Silver  chloride. 

CuO  +     2  HC1         =         CuCl2        -f         H2O. 

Copper  oxide.  .      Copper  chloride. 

If  the  formula  of  silver  chloride  (AgCl)  be  compared  with  that  of 
zinc  chloride  (ZnCl2),  this  difference  will  be  observed  between  them, 
—  that  while  the  molecule  of  silver  chloride  may  be  regarded  as  a 
molecule  of  chlorhydric  acid  (HC1),  in  which  the  atom  of  hydrogen 
(H)  is  replaced  by  an  atom  of  silver  (Ag),  the  molecule  of  zinc 
chloride  must  be  regarded  as  formed  from  two  molecules  of  chlor- 
hydric acid  (H2C12)  by  replacing  two  atoms  of  hydrogen  (H2)  by  one 
atom  of  zinc  (Zn).  Now,  there  is  a  class  of  metals  which,  like  silver, 
replace  hydrogen  atom  for  atom  :  these  metals  are  said  to  be  uni- 
valent.  There  is  another  class  of  metals  which  act  like  zinc  in  re- 
placing hydrogen  :  they  are  said  to  be  bi-valent.  The  same  dis- 
tinction is  seen  in  the  other  compounds  of  these  elements  :  thus, 
sulphuric  acid  being  H2SO4,  zinc  sulphate  is  ZnSO4,  and  silver 
sulphate  is  Ag2SO4;  nitric  acid  being  HNO3,  zinc  nitrate  is 
ZnN2O6,  and  silver  nitrate  is  AgNO3.  It  will  appear  hereafter  that 
there  are  elements  which  are  tri-valent,  quadri-valent,  etc.  In  gen- 
eral terms,  the  replacing-power  of  any  element  with  respect  to 
hydrogen  is  called  its  quantivalence ;  this  quanti valence  of  an 
element  may  be  learned,  not  only  from  the  number  of  hydrogen  atoms 
which  the  atom  of  the  element  can  replace,  but  also  from  the  number 
of  hydrogen  atoms  with  which  it  can  combine  :  thus,  from  the  formula 
of  chlorhydric  acid,  HC1,  we  learn  that  chlorine  is  here  uni-valent.  as 
the  atom  of  chlorine  combines  with  only  a  single  atom  of  hydrogen. 
[See  also  page  288.] 

75.  Aqua  Regia  (Royal  Water). — This  name  was  given  by 
the  alchemists  to  a   mixture   of  chlorhydric  and   nitric   acids, 
because  of  its  power  to  dissolve  gold,  the  "king  of  metals." 
5* 


54  AQUA   REGIA.  —  NASCENT  STATE.  [§76. 

Exp.  29.  —  Place  a  few  square  centimetres  of  genuine  gold-leaf 
at  the  bottom  of  a  test-tube,  and  poiir  upon  the  gold  a  little  strong 
chlorhydric  acid  ;  put  some  gold-leaf  in  a  second  test-tube,  and  pour 
upon  it  a  few  drops  of  nitric  acid  :  neither  acid  attacks  the  gold, 
which  remains  undissolved.  If  the  contents  of  the  two  test-tubes  be 
mixed  together  in  either  tube,  the  gold-leaf  will  almost  immediately 
dissolve. 

The  efficacy  of  aqua  regia  as  a  solvent  of  gold  depends  upon 
the  fact  that  the  nitric  and  chlorhydric  acids  mutually  decom- 
pose each  other.  Chlorine  is  set  free,  and,  as  it  issues  from  its 
combination  with  hydrogen,  acts  on  the  gold  much  more  ener- 
getically than  it  would  in  its  ordinary  condition.  The  chlorine 
in  this  case  is  said  to  be  in  the  nascent  state. 

There  are  numerous  cases  in  which  bodies,  which  do  not  unite 
under  ordinary  conditions,  are  capable  of  chemical  combination  at 
,the  instant  when  they  are  disengaged  from  other  compounds  ;  and  the 
phrase,  "  in  the  nascent  state,"  just  used,  is  one  of  some  convenience, 
although  it  must  not  be  supposed  to  explain,  or  in  any  way  to  account 
for,  the  phenomena  with  reference  to  which  it  is  employed. 

76.  The  practical  importance  of  a  knowledge  of  the  atomic 
weights  in  calculating  the  proportional  amounts  of  the  different 
substances  taking  part  in  any  case  in  a  chemical  action,  has 
already  been  explained  in  §  36,  and  may,  at  this  point,  be  further 
illustrated  as  follows.  In  the  manufacture  of  chlorhydric  acid, 
for  instance,  suppose  it  were  required  to  ascertain  how  much 
sulphuric  acid  would  be  necessary  to  decompose  100  kilos,  of 
salt,  bearing  in  mind  that  the  result  may  be  effected  according  to 
either  of  the  two  actions  formulated  on  page  51. 

The  molecular  wt.  of  NaCl  is  23  +  35.5  =    58.5 

"  "  "          H2SO4  is    2  -f  32  -f-    4X16=    98 

"  «  "          HNaSO4  is    1  -f  23  -f  32  +  64  =  120 

"  "  "          Na2SO4  is  46  -f  32  -f  64  =  142 

"  "  "          HC1  is    1  -j-  35.5  =    36.5 

The  weight  of  the  sulphuric  acid  needed  in  the  two  cases  is 
ascertained  by  solving  the  following  proportions  :  — 


I-".] 


THE  CHLORINE  GROUP. 


55 


First 
reaction 

Second 
reaction 


58.5 

Mol  wt. 

NaCl 

117 

Mol.  wt.  of 
2NaCl 


98 

Mol.  wt. 
H3B04 

98 


=        100       : 

No.  kilos. 

NaCl  used. 

=       100       : 


x  (=  167.52) 

No.  kilos. 
H2SO4  needed. 

x  (=  83.76) 


The  weight  of  chlorhydric  acid  gas  produced  in  the  two  cases 
will  be  precisely  the  same  :  it  is  deduced  from  the  propor- 
tions, — 


nisi  > 
reaction  J 

58.5 
Mol.  wt. 

:      36.5 
Mol.  wt. 

=       100       : 
Kilos. 

x  (=  62.39) 

Kilos. 

NaCl 

HC1 

NaCl  used. 

HC1  produced. 

Second  ) 
reaction  ) 

117 
Mol  wt. 

:        73 

Mol.  wt. 

=       100       : 

x  (=  62.39) 

2NaCl 

2HC1 

The  weights  of  the  residual  sodium  salts  in  the  two  cases  may 
be  deduced  as  follows  :  — 


First    ) 
reaction  ] 

58.5 
Mol.  wt. 

:     120 
Mol  wt. 

=        100       : 
Kilos. 

x  (=  205.13) 
.    Kilos,  of 

NaCl 

HNaSO, 

NaCl  used. 

HNaSO, 

Second  ) 

reaction  ) 

117 

Mol.  wt. 

:      142 

Mol.  wt. 

=       100       : 

x  (=  121.37) 
Kilos,  of 

2NaCl 

Na2S04 

Na2SO4  produced. 

CHAPTER  VIII. 
CHLORINE,  BROMINE,  IODINE  AND  FLUORINE. 

CHLORINE    (cl). 

77.  Chlorine  is  an  abundant  element  and  very  widely  dis- 
tributed in  nature.  It  exists  chiefly  in  combination  with 
sodium  as  sodium  chloride,  which  is  called  rock-salt  or  sea-salt, 
accordingly  as  it  is  found  in  beds  in  the  earth,  or  dissolved  in 
the  water  of  the  ocean.  Every  litre  of  sea- water  will  yield  about 


56  PREPARATION  OF  CHLORINE.  [§  7^ 

5  litres  of  chlorine  gas.  Besides  sodium  chloride,  sea-water  con- 
tains small  quantities  of  the  chlorides  of  several  other  metals ; 
there  are  numerous  minerals,  also,  which  contain  chlorine. 

78.  Chlorine  can  readily  be  prepared  from  chlorhydric  acid 
by  removing  the  hydrogen  of  that  acid  by  chemical  means. 

Exp.  30.  —  In  a  flask  of  about  500  c.c.  capacity,  furnished  with 
a  suitable  delivery-tube,  place  8  or  10  grins,  of  coarsely-powdered 
manganese  binoxide  ;  pour  upon  it  20  or  30  grms.  of  common  muriatic 
acid,  and  gently  heat  the  mixture.  Chlorine  will  soon  be  disengaged, 
and  may  be  recognized  by  its  peculiar  color.  Being  very  heavy,  the 
gas  may  best  be  collected  by  displacement  in  dry  bottles  placed  in 
the  open  air  or  in  a  case  or  box  provided  with  an  efficient  draft.  It 
may  also  be  collected  over  warm  water  or  brine  in  the  water-pan.  It 
can  not  be  well  collected  over  water  at  the  ordinary  temperature,  since 
it  is  rather  easily  soluble  therein  ;  though  the  difficulty  may  be  obvi- 
ated in  part  by  evolving  the  gas  rapidly,  or  by  passing  the  delivery- 
tube  to  the  top  of  the  bottle  in  which  the  gas  is  collected.  It  must 
not  be  left  standing  over  water,  since  it  would  soon  be  entirely  ab- 
sorbed. In  experimenting  with  chlorine,  care  must  always  be  taken 
not  to  inhale  it. 

The  reaction  which  occurs  in  this  experiment  may  be  thus  formu- 
lated :  — 

Mn02  +  4HC1  =  2H20  +  MnCl2  -f  2C1. 

Manganese  binoxide  is  a  substance  rich  in  oxygen,  which,  under 
certain  conditions,  it  readily  yields  up  to  other  elements.  In  the  case 
before  us,  the  oxygen  of  the  manganese  binoxide  unites  with  the 
hydrogen  of  the  chlorhydric  acid  to  form  water.  The  chlorine  of  the 
chlorhydric  acid  unites  in  part  with  the  manganese,  to  form  man- 
ganese chloride,  and  is  in  part  left  free. 

79.  At  the  ordinary  temperature,  chlorine  is  a  gas  of  yellow- 
ish-green color,   2.5   times   heavier  than   atmospheric  air.     Its 
specific  gravity  and  atomic  weight  are  35.5.     It  is  excessively 
irritating   and  suffocating,  even   when   inhaled  in  exceedingly 
small  quantities.     Any  attempt  to  breathe  the  undiluted  gas 
would  undoubtedly  be  fatal. 

80.  Chlorine  is  a  powerful  chemical  agent.     It  combines  with 
hydrogen  with  explosive  violence  when  a  mixture  of  the  two 
gases  is  heated,  or  even  exposed  to  sunlight. 


§  81/ 


PROPERTIES  OF  CHLORINE. 


57 


Exp.  31.  —  In  a  soda-water  bottle,  which  must  be  screened  from 
strong  light  by  wrapping  it  in  a  towel,  unless  direct  and  reflected  sun- 
light be  excluded  from  the  room,  mix  equal  volumes  of  chlorine  and 
hydrogen,  then  remove  the  cork  and  hold  the  mouth  of  the  bottle  in 
the  flame  of  a  lamp.  A  sharp  explosion  will  ensue. 

A  mixture  of  the  two  gases  may  be  kept  in  the  dark  for  any 
length  of  time  without  change  :  in  diffused  daylight,  they 
usually  unite  only  slowly  and  gradually ;  but,  in  direct  sun- 
light, the  union  is  so  instantaneous  as  to  be  attended  with 
explosion. 

81.  Chlorine  combines  also  very  readily  with  many  of  the 
metals,  the  combination  being  in  several  instances  attended 
with  evolution  of  light. 

Exp.  32.  —  Fill  a  bottle  of  at  least  half  a  litre  capacity  with  dry 
chlorine  gas,  by  displace-  Fig.  22. 

ment.  Gradually  sift  a 
gramme  or  two  of  very 
finely-powdered  metallic 
antimony  into  the  bottle. 
The  metal  will  instantly 
take  fire,  and  fall  in  a 
glowing  state  to  the  bot- 
tom of  the  bottle.  This 
fire  attends  the  formation 
of  a  compound  of  chlorine 
and  antimony,  a  portion 
of  which  will  be  seen  per- 
vading the  bottle  as  a  white  smoke. 

It  is  necessary,  for  the  success  of  this  experiment,  that  the  gas  be 
thoroughly  dried  ;  this  is  effected  by  heating  the  flask  containing 
the  manganese  binoxide  and  chlorhydric  acid  gently,  and  passing  the 
chlorine  through  a  tube  filled  with  chloride  of  calcium.  (Appendix, 
§  16.)  It  is  not  amiss  to  interpose  a  small  bottle  between  the  flask 
and  the  drying-tube  :  this  bottle  may  be  kept  cool  by  immersion  in 
water,  and  will  retain  a  considerable  portion  of  the  moisture  carried 
forward  by  the  gas. 

This  experiment,  and,  indeed,  all  experiments  with  chlorine,  should 
be  performed  only  in  places  where  there  is  a  current  of  air  sufficiently 


58  PROPERTIES  OF  CHLORINE.  [§  82. 

powerful  to  carry  away  from  the  operator  the  volatile  products  of  the 
reaction,  together  with  any  chlorine  which  may  escape  from  the  bottle. 

As  in  the  case  of  the  union  of  sulphur  with  copper  (Exp.  1, 
§  2),  so  here  it  will  be  seen  that  burning,  as  commonly  under- 
stood, is  in  no  wise  peculiar  to  the  union  of  oxygen  with  the 
other  elements.  -In  the  act  of  chemical  combination,  heat  is 
always  evolved,  and,  of  course,  light  as  well,  if  particles  of  solid 
matter  be  present,  and  become  hot  enough  to  be  luminous. 

Since  oxygen  is  very  abundant,  we  are  more  accustomed  to 
witness  exhibitions  of  its  chemical  action  than  of  that  of  any 
other  element ;  but  we  must  not,  therefore,  lose  sight  of  the  fact 
that  among  the  elements,  there  are  several  which  possess  chemi- 
cal power  as  great  when  brought  into  play,  though  not  as  fre- 
quently exhibited  as  that  of  oxygen. 

82.  A  burning  jet  of  hydrogen,  on  being  introduced  into  a 
jar  of  chlorine,  will  continue  to  burn  with  a  peculiar  green 
light,  the  two  gases  uniting  to  form  chlorhydric  acid ;  and, 
by  reversing  the  experiment,  chlorine  may  just  as  well  be  burned 
in  an  atmosphere  of  hydrogen.  Although  chlorine  is  thus  both 
combustible  and  a  supporter  of  combustion,  as  far  as  hydrogen 
is  concerned,  it  does  not  unite  directly  with  either  oxygen  or 
carbon. 

If  a  bit  of  paper,  attached  to  a  wire,  be  dipped  in  hot  oil  of  turpen- 
33.  tine,  and  then  quickly  plunged  into  a  bottle  of  chlo- 
rine, it  will  usually  take  fire  spontaneously,  and  burn 
with  evolution  of  dense  black  fumes.  On  account 
of  the  volatility  and  ready  inflammability  of  oil  of 
turpentine,  it  is  best  heated  upon  a  water-bath  (Ap- 
pendix, §  17),  in  a  porcelain  dish. 

Exp.  33.  —  Thrust  a  burning  taper,  or  a  bit  of 
naming  wood  or  paper,  into  a  bottle  of  chlorine  gas  ; 
the  flame  will  become  murky,  and,  after  struggling 
for  a  moment,  will  go  out.  Much  smoke  is  at  the 
same  time  given  off. 

The  wax,  wood,  paper  and  turpentine  of  the  fore- 
going experiments,  and,  indeed,  most   of  the   sub- 
stances ordinarily  used  as  combustibles,  contain  hydrogen  and  carbon. 


§  83.]          PROPERTIES  OF  CHLORINE.  59 

The  hydrogen  of  these  substances  will  burn  in  chlorine,  that  is,  will 
unite  chemically  with  the  chlorine  to  form  chlorhydric  acid  ;  but  the 
carbon  will  not  thus  unite  with  chlorine.  Hence  it  is  that  in  the  ex- 
periments in  question  the  combustion  is  at  the  expense  of  the  hydro- 
gen ;  the  hydrogen  of  the  candle,  turpentine  and  so  forth,  alone 
unites  with  chlorine  ;  while  the  carbon  is  set  free  as  lamp-black  or 
smoke. 

83.  Chlorine  is  a  powerful  bleaching  agent,  and,  on  this 
account,  is  of  great  importance  in  the  arts.  The  chlorine  to 
be  used  for  this  purpose  must  be  moist  :  perfectly  dry  chlorine 
will  not  bleach. 

This  may  be  illustrated  by  passing  perfectly  dry  chlorine  through  a 
glass  tube  filled  with  bits  of  colored  calico.  The  coloring  matters 
will  not  be  destroyed  so  long  as  they  remain  dry  ;  but  if,  after  the  dry 
chlorine  has  been  allowed  to  act  for  a  few  minutes,  a  little  water  be 
poured  into  the  tube,  so  that  its  contents  may  be  moistened,  they  will 
be  bleached  at  once. 

Those  coloring  matters  which  are  of  vegetable  or  animal  origin  are, 
for  the  most  part,  complex  compounds  of  carbon,  hydrogen,  nitrogen 
and  oxygen.  When  moist  chlorine  is  brought  into  contact  with  them, 
a  somewhat  complicated  reaction  occurs  :  a  portion  of  their  hydrogen 
is,  no  doubt,  taken  out  by  the  chlorine  ;  but,  at  the  same  time,  some  of 
the  water  which  is  present  is  decomposed,  and  its  oxygen  assists  the 
disorganization  of  the  compound  which  is  to  be  destroyed.  As  a  rule, 
the  coloring  matters  are  far  more  easily  oxidized  than  the  cotton 
cloth  ;  hence  they  can  readily  be  removed  by  the  action  of  chlorine 
without  injury  to  the  cloth.  But,  if  the  action  of  the  chlorine  were 
to  be  continued  after  the  coloring  matter  had  been  destroyed,  the 
cloth  itself  would  gradually  be  burned  up. 

The  bleaching  properties  of  chlorine  may  be  conveniently  illus- 
trated by  means  of  an  aqueous  solution  of  chlorine,  chlorine- 
water,  which  may  be  prepared  by  connecting  the  flask  in  which 
the  gas  is  generated  with  a  series  of  Woulfe-bottles,  as  in  the  prepa- 
ration of  chlorhydric  acid.  (Fig.  21,  §  72.) 

Exp.  34.  —  Pour  into  a  small  bottle  a  quantity  of  chlorine- water, 
drop  into  it  a  small  quantity  of  a  solution  of  indigo,  and  stir  the 
mixture  with  a  glass  rod.  The  blue  color  of  the  indigo  will  be  imme- 
diately destroyed. 

In  the  same  way,  the  color  of  litmus,  cochineal,  aniline-purple,  or 


GO  CHLOklNE  AND  OXYGEN.  [§  84. 

of  flowers,  calico,  and  the  like,  can  be  readily  destroyed  by  immersion 
in  chlorine-water. 

84.  Chlorine  is  also  employed  as  a  disinfectant.     It  destroys 
noxious  effluvia,  either  by  acting  on  them  as  on  coloring  matters, 
or  by  simply  taking  away  hydrogen,  as  in  the  case  of  sulphuret- 
ted hydrogen,  hereafter  to  be  studied. 

85.  Oxides  and  Acids  of  Chlorine.  —  Five  compounds  of 
oxygen  and  chlorine  are  recognized  by  chemists,  although  they 
have  not  all  been  isolated.     Four  of  them  combine  with  the 
elements  of    water  to  form   acids.     Of   these    compounds   the 
most  important  is  chloric  acid  (HC1O3)  corresponding  to  nitric 
acid  (HNO3),  and  giving  rise  to  compounds    called  chlorates. 
Potassium    chlorate    (KC1O3),    one    of   these    compounds,    was 
used  in  Exp.  4,  §  12,  as  a  source  of  oxygen.     Under  the  in- 
fluence of  heat,  it  is  decomposed  into  oxygen   and  potassium 
chloride  :  KC1O3  =  KC1  +  O3. 

One  of  the  salts  of  hypochlorous  acid  (HC1O),  namely, 
calcium  hypochlorite,  is  of  great  importance  in  the  arts, 
being  an  ingredient  of  "  chloride  of  lime,"  or  bleaching'- 
powder.  This  substance  is  used  in  very  large  quantities  for 
bleaching  purposes  :  its  value  depends  upon  the  readiness  with 
which  it  gives  off  chlorine  under  the  influence  of  chemical 
agents.  When  it  is  treated  with  any  acid,  chlorine  is  disen- 
gaged. 

Exp.  35.  —  At  the  bottom  of  a  large,  tall  beaker,  or  other  wide-- 
mouthed glass  vessel,  of  the  capacity  of  two  or  three  litres,  place  a 
small  bottle  containing  15  or  20  grms.  of  bleaching-powder.  Cover 
the  beaker  with  a  glass  plate,  or  sheet  of  pasteboard,  provided  with  a 
small  hole  at  the  centre  :  through  this  hole  in  the  cover  pass  a  thistle- 
tube  down  into  the  bottle  of  bleaching-powder,  and  pour  upon  it 
several  small  successive  portions  of  sulphuric  acid  diluted  with  an 
equal  volume  of  water.  Chlorine  gas  will  immediately  be  set  free 
from  the  bleaching-powder,  and,  falling  over  into  the  bottom  of  the 
large  beaker,  will  gradually  press  out  and  displace  the  air  therein 
contained,  so  that,  after  a  short  time,  the  beaker  will  be  seen  to  be 
completely  filled  with  the  green  gas.  This  is  by  far  the  easiest  and 
most  expeditious  method  of  preparing  chlorine.  The  heavy  gas  may 


I  88.]  BROMINE.  61 

be  ladled  out  of  the  jar  with  a  dipper  made  of  any  small  bottle,  and 
poured  upon  a  solution  of  indigo  to  show  its  bleaching  power. 

Exp.  36.  —  Soak  a  bit  of  printed  calico  in  a  half-litre  of  water,  into 
which  10  or  15  grms.  of  bleaching-powder  have  been  stirred.  Observe 
that  the  color  of  the  calico  slowly  undergoes  change  ;  then  transfer 
the  cloth  to  another  bottle  filled  with  very  dilute  chlorhydric  or 
sulphuric  acid,  and  take  note  of  the  rapidity  with  which  the  color  is 
discharged.  If  need  be,  again  immerse  the  calico  in  the  bleaching 
bath,  and  afterwards  in  the  dilute  acid.  Finally,  wash  the  whitened 
cloth  thoroughly  in  water. 

BROMINE  (BP). 

86.  Bromine  is  an  element  closely  allied  to  chlorine,     It  is 
found  in  small  quantities  in  sea-water  and  in  the  water  of  many 
saline  springs.      One  litre  of  sea-water  contains  from  0.0143 
to  0.1005  grin,  of  it.     As  it   exists  in  nature,  it  is  combined 
with  metals,   magnesium   bromide  being   the   compound  most 
commonly   met   with.      Magnesium   bromide  is   a   constituent 
of  the   uncrystallizable  residue,   called  bittern,   which  remains 
after  the  sodium  chloride  has  been  crystallized  out  from  the 
natural  brines  :  at  several  saline  springs  this  bittern  contains  so 
large  a  proportion  of  the  bromide,  that  bromine  can  be  profitably 
extracted  from  it.     Most  of  the  bromine  of  commerce  is  thus 
obtained. 

87.  At  the  ordinary  temperature,  bromine  is  a  liquid  of  dark 
brown-red  color,  about  three  times  as  heavy  as  water,  and  highly 
poisonous.     Its  odor  is  irritating  and  disagreeable,  whence  the 
name  bromine,  derived  from  a  Greek  word  signifying  a  stench. 
It  boils  at  about  60°,  but  is  very  volatile  even  at  the  ordinary 
temperature  of  the  air. 

Exp.  37.  —  By  means  of  a  small  pipette,  throw  into  a  flask  01 
bottle  of  1  or  2  litres'  capacity  3  or  4  drops  of  bromine.  Cover 
the  bottle  loosely,  and  leave  it  standing.  In  a  short  time  it  will  be 
filled  with  a  red  vapor,  which  is  bromine  gas.  This  vapor  is  very 
heavy,  more  than  5  times  as  heavy  as  air  and  80  times  heavier  than 
hydrogen. 

88.  In  its  chemical  behavior,  as  well  as  in  many  of  its  physi« 
cal  properties,  bromine  closely  resembles  chlorine. 


62  tOblfrti.  [§  89. 

Its  affinity  for  hydrogen,  though  weaker  than  that  of  chlorine,  is 
still  powerful.  Like  chlorine,  it  is  an  energetic  bleaching  arid  disin- 
fecting agent.  If  finely-powdered  metallic  antimony  be  thrown  into 
bromine,  violent  chemical  action  takes  place.  The  metal  burns  as  in 
chlorine,  antimony  bromide  being  formed. 

89.  Bromhydric  Acid  (HBr).  —  Like  chlorine,  bromine  forms 
with  hydrogen  a  compound  in  which  equal  volumes  of  the  two 
elements  (the  bromine  being  in  the  state  of  vapor)  are  united 
without  condensation.  Bromhydric  acid  is  a  colorless,  irritating 
gas,  readily  soluble  in  water. 

Bromic  acid  ^HBrO3)  is  analogous  to  chloric  acid  (HC1O,). 
The  bromates  resemble  the  corresponding  chlorates. 


IODINE  (i). 

90.  In  its  chemical  properties  iodine  bears  a  striking  resem- 
blance to  bromine,  and  consequently  to  chlorine  also.     It  exists 
in  sea-water  and  in  the  water  of  many  saline  and  mineral  springs. 
The  proportion  of  iodine  in  sea- water  is  exceedingly  small,  being 
even  smaller  than  that  of  bromine  ;  but  iodine  is  obtained  more 
readily  than  bromine  ;  for  iodine  is  absorbed  from  sea- water  by 
various  marine  plants,  which,  during  their  growth,  collect  and 
concentrate  the  minute  quantities  of  iodine  which  the  sea-water 
contains,  to  such  an  extent  that  it  can  be  extracted  from  them 
with  profit 

91.  At  the    ordinary  temperature,   iodine   is   a   soft,   heavy, 
crystalline  solid  of  bluish-black  color  and  metallic  lustre.     Its 
specific  gravity  is  4.95.     It  evaporates  rather  freely  at  the  or- 
dinary temperature  of  the  air,  and  the  more  rapidly  when  it  is 
in  a  moist  condition.     Its  odor  is  peculiar,  somewhat  resembling 
that  of  chlorine,  but  weaker,  and  easily  distinguished  from  it. 
It  is  but  slightly  soluble  in  water,  but  dissolves  readily  in  alco- 
hol.    The  atomic  weight  of  iodine  is  127. 

The  vapor  of  iodine  is  of  a  magnificent  purple  color,  whence 
the  name  iodine,  derived  from  a  Greek  word  signifying  violet- 
colored.  This  vapor  is  very  heavy,  —  indeed,  the  heaviest  of 


§  93.]  TESTS  FOR  IODINE  AND  CHLORINE.  63 

all  known  gases  :  it  is  nearly  9  times  as  heavy  as  air  :  its  specific 
gravity  referred  to  hydrogen  is  127. 

Exp.  38.  —  Hold  a  dry  test-tube  in  the  gas-lamp  by  means  of  the 
wooden  nippers,  and  warm  it  along  its  entire  length,  in  so  far  as  this 
is  practicable.  Drop  into  the  hot  tube  a  small  fragment  of  iodine  and 
observe  the  vapor  as  it  rises  in  the  tube.  If  only  a  small  portion  of 
the  tube  were  heated,  the  vapor  would  be  deposited  as  solid  iodine 
upon  the  cold  part  of  its  walls. 

92.  Solid  iodine  is  never  met  with  in  the  amorphous,  shape- 
less state  in  which  glass,  resin,  coal  and  many  other  substances, 
occur.     No  matter  how  obtained,  its  particles  always  exhibit  a 
definite  crystalline  structure.     If  the  iodine  be  melted,  and  then 
allowed  to  cool,  or  if  it  be  converted  into  vapor  and  this  vapor 
be  subsequently  condensed,  crystals  will  be  formed  in  either 
case. 

93.  A  singular  property  of  iodine  is  its  power  of  forming  a 
blue  compound  with  starch. 

Exp.  39.  —  Prepare  a  quantity  of  thin  starch  paste  by -boiling  30 
c.  c.  of  water  in  a  porcelain  dish,  and  stirring  into  it  0.5  grm.  of  starch 
which  has  previously  been  reduced  to  the  consistency  of  cream  by 
rubbing  it  in  a  mortar  with  a  few  drops  of  water. 

Pour  3  or  4  drops  of  the  paste  into  10  c.  c.  of  water  in  a  test-tube, 
and  shake  the  mixture  so  that  the  paste  may  be  equably  diffused 
through  the  water,  then  add  a  drop  of  an  aqueous  solution  of  iodine, 
and  observe  the  beautiful  blue  color  which  the  solution  assumes.  If 
the  solution  be  heated,  the  blue  coloration  will  disappear,  but  it  re- 
appears when  the  liquid  is  allowed  to  cool. 

Dip  a  strip  of  white  paper  in  the  starch-paste  and  suspend  it,  while 
still  moist,  in  a  large  bottle,  into  the  bottom  of  which  two  or  three 
crystals  of  iodine  have  been  thrown.  As  the  vapor  of  iodine  slowly 
diffuses  through  the  air  of  the  bottle,  it  will  at  last  come  in  contact 
with  the  starch,  and  after  some  minutes  the  paper  will  be  colored 
blue. 

This  reaction  furnishes  a  very  delicate  test  for  iodine.  By 
its  means  it  has  been  proved  that  iodine,  though  nowhere  very 
abundant,  is  very  widely  distributed  in  nature.  This  reaction  is 
also  made  the  basis  of  a  test  for  chlorine.  Strips  of  paper  are 


64  COMPOUNDS  OF  IODINE.  [§  94. 

smeared  with  starch-paste  into  which  potassium  iodide  in  solution 
has  been  stirred.  The  paper  is  dried  and  kept  in  stoppered 
bottles.  When  a  strip  of  this  pap'er  is  moistened  and  exposed  to 
chlorine  gas,  the  chlorine  attacks  the  potassium  iodide,  potassium 
chloride  is  formed,  and  iodine  is  set  free.  The  iodine  thus  set 
free  manifests  itself  by  imparting  the  characteristic  blue  color  to 
the  starch:— KI  +  Cl  =  KC1  + 1. 

94.  As  has  been  already  stated,  iodine,  in  its  chemical  be- 
havior,  resembles  chlorine  and  bromine,   only  its  affinities  are 
more  feeble.     It  enters  into  combination  with  less  energy  than 
either  of  these  elements,  and  is  displaced  by  them  from  most 
of  its  combinations.     Like  them,   it  unites  directly  with   the 
metals  and  with  several  other  elements.     It  gradually  corrodes 
organic  tissues,  and  destroys  coloring-matters,  though  but  slowly. 
Iodine  and  certain  of  its  compounds  are  much  used  in  medicine 
and  in  photography. 

95.  lodohydric  acid  (Hi)  is  a  colorless  acid   gas  of  suffo- 
cating odor,  very  soluble  in  water.      It  is  made  up  of  equal 
volumes  of  hydrogen  and  iodine  vapor.      The  proportions  by 
weight  are   1   part  of  hydrogen  to   127  parts  of  iodine.      The 
chemical  effect  of  the  small  proportion  of  hydrogen  contained 
in  iodohydric  acid  is  most  remarkable.     Only  T£F,  or  less  than 
1  per  cent  of  iodohydric  acid  is  hydrogen ;  yet  this  very  small 
proportional  quantity  of  hydrogen  is  competent  to  impart  to  the 
new  compound  properties  possessed  by  neither  the  iodine  nor 
the  hydrogen  :   the  acid  bears  no  resemblance  to  either  of  its 
constituents. 

lodic  acid  (HIO,)  is  analogous  to  chloric  and  bromic  acids. 
The  iodates  correspond  in  composition  and  general  character  to 
the  bromates  and  chlorates, 

96.  Nitrogen  Iodide,  —  Mtrogen  forms,  with  chlorine,  bro- 
mine and  iodine,  a  class  of  compounds  which  are  very  explosive. 
Nitrogen  chloride  is  extremely  dangerous,  often  exploding  spon- 
taneously  without   apparent   cause.     Nitrogen  iodide  is  much 
less  explosive  and  may  safely  be  prepared  in  very  small  quan- 
tities. 


§  97.]  THE  CHLORINE  GROUP.  65 

Exp.  40.  —  Place  0.25  grm.  of  finely-powdered  iodine  in  a  porce- 
lain capsule,  pour  upon  it  enough  concentrated  ammonia- water  to 
somewhat  more  than  cover  the  iodine  and  allow  the  mixture  to  stand 
during  15  or  20  minutes.  Collect  in  several  small  filters  (Appen- 
dix, §  15)  the  insoluble  dark  brown  powder  which  will  be  found  at 
'Jae  bottom  of  the  liquid.  Wash  well  with  cold  water  and  then 
remove  the  filters,  together  with  their  contents,  from  the  funnels  ;  pin 
them  upon  bits  of  board,  and  allow  them  to  diy  spontaneously.  The 
powder  is  the  nitrogen  iodide.  As  soon  as  it  has  become  thoroughly 
dry,  it  will  explode  upon  being  rubbed,  even  with  a  feather,  or  jarred, 
as  by  the  shutting  of  a  door,  or  by  a  blow  upon  the  wall  or  table. 

97.  The  Chlorine  Group.  —  Chlorine,  bromine  and  iodine 
constitute  one  of  the  most  remarkable  and  best-defined  natural 
groups  of  elements.  Whether  we  regard  the  uncombined  ele- 
ments or  their  compounds,  it  is  impossible  not  to  be  struck  with 
the  close  analogies  which  subsist  between  them. 

With  hydrogen,  all  of  these  elements  unite  in  the  propor- 
tion of  one  volume  to  one  volume,  without  condensation,  to 
form  acid  compounds  extremely  soluble  in  water  and  pos- 
sessing throughout  analogous  properties.  Moreover,  each  of 
them  forms  a  powerful  acid  containing  three  atoms  of  oxy- 
gen, besides  divers .  other  compounds  of  obvious  likeness. 
With  nitrogen  they  all  form  explosive  compounds.  Many 
similar  analogies  will  be  made  manifest  as  we  proceed  to  study 
the  other  elements  and  their  compounds  with  this  chlorine 
group. 

There  is  a  family  resemblance  between  these  three  elements 
as  regards  their  physical  as  well  as  their-  chemical  charac- 
teristics ;  but  with  all  their  properties,  a  distinct  progression 
is  observable  from  chlorine  through  bromine  to  iodine.  At 
the  ordinary  temperature,  chlorine  is  a  gas,  bromine  a  liquid 
and  iodine  a  solid,  though,  at  temperatures  not  widely  apart, 
they  are  all  known  in  the  gaseous  and  liquid  states.  The 
specific  gravity  of  bromine  vapor  is  greater  than  that  of  chlo- 
rine, and  that  of  iodine  greater  than  that  of  bromine.  Chlorine 
gas  is  yellow,  the  vapor  of  bromine  is  reddish-brown,  that  of 
iodine  violet.  So  with  all  their  other  properties,  —  chlorine  will 


66  FLUORINE.  [§98. 

be  at  one  end  of  the  scale,  iodine  at  the  other,  while  bromine 
invariably  occupies  the  intermediate  position. 

The  properties  of  the  members  of  this  group  illustrate  what 
seems  to  be  a  general  principle ;  namely,  that  among  the  mem- 
bers of  a  natural  chemical  group,  chemical  energy  varies  in  the 
inverse  direction  of  the  atomic  weights.  Thus,  the  atomic 
weight  of  chlorine  is  35.5,  that  of  bromine  80  and  that  of  iodine 
127  j  while  the  chemical  energy  of  these  elements  follows  the 
opposite  order. 

FLUORINE   (F). 

98.  There   is   another   substance,   called   fluorine,  which  is 
closely  analogous  to  chlorine.     It  occurs  tolerably  abundantly 
in  nature  as  calcium  fluoride  (CaP2),  in  the  mineral  known  as 
fluor-spar.     Small  quantities  of  fluorine  are  found  also  in  several 
other  minerals,  in  vegetable  and  animal  substances,  particularly 
in  bones,  and  traces  of  it  occur  in  sea- water  and  in  various  rocks 
and  soils.     Of  late  years  a  considerable  mine  of  a  fluorine  min- 
eral called  cryolite  (fluoride  of  sodium  and  aluminum)  has  been 
worked  in  Greenland. 

99.  Fluorine  can  not  be  readily  obtained  in  the  free  state  and 
scarcely  any  thing  is  known  of  it  in  that  condition.     Of  all  the 
elements,  it  appears  to  have  the  strongest  tendency  to  enter  into 
chemical  combination.     It  is  not  only  difficult  to  expel  fluorine 
from  the  minerals  in  which  it  is  found  in  nature ;  but.,  on  being 
set  free  from  one  compound,  it  immediately  attacks  whatever 
substance  is  nearest  at  hand,  and  so  enters  into  a  new  combina- 
tion.    Hence  it  is  wellnigh  impossible  to  collect  it.     Little  or 
no  doubt,  however,  is  entertained  as  to  the  general  nature  of 
fluorine,   since  its  compounds  are    closely  analogous   in   many 
respects  to  the  corresponding  compounds  of  chlorine,  bromine 
and  iodine.     It  is  to  be  remarked  that  fluorine  is  the  only  ele- 
ment  known   which  forms  no  compound  with   oxygen.     The 
symbol  of  fluorine  is  F.     Its  atomic  weight  is  19. 

100.  Fluorhydric   Acid   (HP). — With    hydrogen,   fluorine 
forms  a  powerful  acid  corresponding  to  chlorhydric  acid  and  the 


§  100.]  FLUORHYDRW  ACID.  67 

other  hydrides  of  the  chlorine  group.  It  is  a  more  energetic 
acid  than  either  of  these,  but  is  specially  characterized  by  its 
corrosive  action  upon  glass.  It  may  be  readily  prepared  by 
distilling  powdered  fluor-spar  with  strong  sulphuric  acid ;  the 
reaction  being  analogous  to  that  which  occurs  when  common  salt 
is  treated  with  sulphuric  acid  :  — 

CaF2  -f  H2SO,  =  CaSO,  -f  2HF. 

Since  the  acid  rapidly  corrodes  glass,  the  process  must  be  con- 
ducted in  metallic  vessels.  Ordinarily,  retorts  of  lead  or  plati- 
num are  employed,  and  the  distillate  is  collected  in  receivers 
made  of  the  same  metals,  and  carefully  cooled  by  means  of  ice. 

The  acid  thus  prepared  always  contains  a  small  amount  of 
water  which  it  is  difficult  to  remove  completely.  The  perfectly 
dry  acid,  which  may  be  made  by  the  distillation  of  dry  hydrogen 
potassium  fluoride  is,  like  that  prepared  as  above,  a  very  volatile, 
fuming  liquid ;  it  does  not,  however,  act  upon  glass. 

This  corrosive  power,  possessed  by  moist  fluorhydric  acid 
gas,  as  well  as  by  its  aqueous  solution,  is  made  use  of  for  etch- 
ing glass.  The  graduations  on  the  glass  stems  of  thermometers 
and  eudiometers  may  thus  be  made  with  great  precision  and 
facility  :  the  acid  is  largely  employed  also  in  ornamenting  glass 
with  etched  patterns. 

Exp.  41.  —  Warm  a  slip  of  glass,  and  rub  it  with  beeswax  so  that 
it  shall  be  everywhere  covered  with  a  thin,  uniform  layer  of  the  wax. 
With  a  needle,  or  other  pointed  instrument,  write  a  name,  or  trace 
any  outline  through  the  wax,  so  as  to  expose  a  portion  of  the  glass. 
Lay  the  etching,  face  downward,  upon  a  bowl  or  trough  of  sheet-lead, 
in  which  has  been  placed  a  teaspoonful  of  powdered  fluor-spar  and 
enough  strong  sulphuric  acid  to  convert  it  into  a  thin  paste. 

Cover  the  glass  and  the  top  of  the  dish  with  a  sheet  of  paper  and 
then  gently  heat  the  leaden  vessel  for  a  few  moments,  taking  care  not 
to  melt  the  wax  ;  then  set  the  dish  aside  in  a  warm  place  and  leave  it 
at  rest  during  an  hour  or  two.  Finally,  melt  the  wax  and  wipe  it  off 
the  glass  with  a  towel  or  bit  of  paper  ;  the  glass  will  be  found  to  be 
etched  and  corroded  at  the  places  where  it  was  laid  bare  by  the  re- 
moval of  thp  wax. 


66  OZONE.  [§  101. 

CHAPTEE   IX. 
OZONE. 

101.  Besides  ordinary  oxygen,  such  as  is  found  in  the  air  and 
has  been  prepared  in  Exps.  3  and  4,  another  kind  or  form  of 
this  element  is  known  to  chemists.     This  new  modification  of 
oxygen  has  received  a  special  name,  and  is  called  ozone. 

Several    other  elements,   notably   sulphur,    phosphorus    and 

carbon,  occur,  as  oxygen  does,  in  very  unlike  states,  or  with  verv 
different  attributes,  while  the  fundamental  chemical  identity  of  the 
substance  is  preserved.  The  word  allotropism  is  employed  to 
express  this  capability  of  some  of  the  elements  :  it  is  derived  from 
Greek  words  signifying  of  a  different  habit  or  character.  This  word 
serves  merely  to  bring  into  one  category  a  considerable  number  of 
conspicuous  facts,  of  whose  essential  nature  we  have  no  knowledge  ; 
there  is,  of  course,  no  virtue  in  the  word  itself  to  explain  or  account 
for  the  phenomena  to  which  it  refers. 

102.  Ozone    is    an    exceedingly    energetic     chemical    agent 
which   resembles   chlorine  in  some  respects  :   it  can  therefore 
be   advantageously   studied   in   connection   with    the    chlorine 
group. 

It  was  long  ago  noticed  that  when  an  electrical  machine 
was  put  in  operation  a  peculiar,  pungent  odor  was  developed. 
More  recently  it  has  been  observed  that  the  same  odor  is  mani- 
fested during  the  electrolysis  of  water  (§  25),  and  that  this  odor 
resembles  that  evolved  by  moistened  phosphorus  when  exposed 
to  the  air.  It  has  gradually  been  made  out,  that  the  odor  in 
each  of  these  cases  is  due  to  the  presence  of  a  peculiar  modifica- 
tion of  oxygen,  called  ozone  from  a  Greek  word  signifying  to 
smell. 

103.  Ozone  may  be  best  prepared  by  certain  electrical  ma- 
chines devised  for  the   purpose  ;    but  the   phosphorus  method 
will  usually  be  found  most  convenient. 


§  104.]  PROPERTIES  OF  OZONE.  69 

Exp.  42.  —  In  a  clean  bottle  of  1  or  2  litres'  capacity  place  a  piece 
of  phosphorus  2  or  3  c.  m.  long,  the  surface  of  which  has  been  scraped 
clean  (under  water)  with  a  knife  ;  pour  water  into  the  bottle  until 
the  phosphorus  is  half  covered  ;  close  the  bottle  with  a  loose  stop- 
per, and  set  it  aside  in  a  place  where  the  temperature  is  20°  or  30°. 
In  the  course  of  ten  or  fifteen  minutes  a  column  of  fog  will  be  seen 
to  rise  from  that  portion  of  the  phosphorus  which  projects  above  the 
water  :  the  original  garlic  odor  of  the  phosphorus  will  soon  be  lost, 
and  the  peculiar  odor  of  ozone  will  gradually  pervade  the  bottle. 
After  one  or  two  hours,  the  bottle  will  be  found  to  contain  an  abun- 
dance of  ozone  for  purposes  of  illustration. 

The  chemical  changes  which  occur  during  this  experiment  are 
complicated  ;  it  will  be  enough  to  say  of  them  that  the  phosphorus 
unites  with  oxygen  from  the  air  in  the  bottle  to  form  an  oxide  of 
phosphorus,  that  during  this  process  of  oxidation  a  portion  of 
the  oxygen  in  the  bottle  is  changed  into  ozone,  and  that  some  of  the 
ozone  remains,  even  after  several  hours,  diffused  in  the  air  of  the 
bottle. 

It  must  be  distinctly  understood  that  only  a  very  minute 
quantity  of  ozone  is  obtained  in  the  foregoing  .experiment ; 
but  ozone  is  a  substance  possessing  great  chemical  power,  and- 
but  little  of  it  is  needed  in  order  to  exhibit  its  characteristic 
properties. 

104.  Ozone  is  an  irritating,  poisonous  gas  :  air  which  is 
highly  charged  with  it  is  irrespirable,  and  produces  effects  on 
the  human  subject  similar  to  those  produced  by  chlorine.  Its 
odor,  which  has  been  compared  to  that  of  weak  chlorine,  is  so 
powerful  that  it  can  be  recognized  in  air  containing  only  one- 
millionth  part  of  the  gas.  Like  chlorine,  ozone  bleaches  and 
destroys  vegetable  coloring  matters,  and  is  a  powerful  disin- 
fectant. Like  chlorine,  it  instantly  decomposes  the  iodides  of 
the  metals  ;  upon  this  property  is  based  a  ready  method  of 
testing  for  its  presence. 

Exp.  43.  —  Into  the  bottle  of  ozonized  air  (Exp.  42),  thrust  a 
moistened  slip  of  test-paper,  saturated  with  starch  and  iodide  of 
potassium,  prepared  as  described  in  §  93  :  the  paper  will  instantly 
acquire  a  deep  blue  tint. 


70  OXIDIZING  POWER  OF  OZONE.  [§  1Q6. 

As  in  the  case  where  the  test-paper  is  employed  for  detecting 
chlorine  (§  93),  so  here,  the  reaction  depends  upon  the  displacement 
of  the  chemically  feeble  iodine  by  the  more  powerful  ozone  :  — 

2KI  +  0=  K20  -f  21. 

The  ozone  here  acts  as  oxygen,  in  one  sense  :  at  all  events,  the  potas- 
sium oxide  formed  is  not  to  be  distinguished  from  potassium  oxide 
prepared  with  common  oxygen  ;  but  this  in  no  wise  contradicts  the  fact 
that  ozone  is  an  extraordinarily  active  and  energetic  variety  of  oxy- 
gen, inasmuch  as  common  oxygen  will  not  effect  this  decomposition. 

105.  The  great  difference  between  ordinary  oxygen  and  the  allo- 
tropic  modification,  ozone,  is  generally  explained  by  supposing  that 
while  the  molecules  of  oxygen  and  the  molecules  of  ozone  are  both 
made  up  of  oxygen  atoms,  the  former  contains  two  atoms  in  each  mole- 
cule (see  page  90.  ),  while  the  latter  contains  three  atoms.  This  idea 
is  strengthened  by  the  fact  that  when  oxygen  is  converted  into  ozone 
a  condensation  takes  place,  and  when  the  ozone  is  reconverted  into 
ordinary  oxygen  there  is  an  expansion  to  the  original  bulk.  Other 
observed  facts  lead  to  the  same  conclusion,  and  the  action  of  ozone  on 
potassium  iodide  would  probably  be  more  correctly  expressed  by  this 
equation  : 


106.  The  oxidizing  power  of  ozone  is  intense.  When 
moisture  is  present,  it  oxidizes  all  the  metals  excepting  gold, 
platinum  and  the  platinum  metals  :  even  silver  is  oxidized  by 
it  at  the  ordinary  temperature,  and  becomes  covered  with  a 
brown  coating  of  an  oxide  of  silver.  In  like  manner-,  most 
organic  substances  are  quickly  oxidized  by  ozone  :  when  sub- 
stances such  as  saw-dust,  garden-mould,  powdered  charcoal, 
milk  or  flesh,  are  thrown  into  a  bottle  of  ozonized  air,  the  odor 
of  ozone  instantly  disappears. 

By  virtue  of  this  strong  oxidizing  power,  ozone  is  of  great 
importance  as  a  disinfecting  agent.  It  destroys  instantly  a 
multitude  of  offensive  gases,  such  as  arise  from  decaying  animal 
and  vegetable  matter,  and  has  been  frequently  recommended  of 
late  as  a  substance  well  fitted  for  the  purification  of  sick-rooms 
and  hospital-  wards. 


109.] 


ANTOZONE  CLOUDS.  —  SULPHUR. 


107.  A  minute  proportion  of  ozone  seems  to  exist  in  normal 
atmospheric  air  :  it  is  especially  abundant  after  a  thunder-storm. 
It  is  seldom  found  in  the  air  of  thickly  inhabited  locali- 
ties. At  temperatures  above  100°  ozone  is  converted  into  ordi- 
nary oxygen. 

108.  Antozone.  During  the  oxidation  of  phosphorus  in  moist 
air,  Exp.  42,  it  was  no  doubt  noticed  that  the  bottle  became 
filled  with  white  fumes.  Also  in  Exp.  7,  §  17,  during  the  rapid  oxi- 
dation of  phosphorus  there  was  produced  a  white  mist  of  considerable 
permanence,  which  remained  long  after  the  oxides  of  phosphorus, 
which  were  also  formed,  had  been  absorbed  by  the  water.  More- 
over, if  electrized  oxygen  (or  electrized  air)  be  passed  through  a 
solution  of  potassium  iodide,  the  ozone  will  be  completely  removed  ; 
if,  subsequently,  the  air  or  oxygen  be  allowed  to  bubble  through 
water,  the  same  peculiar  mist  will  be  formed.  It  was  for  a  time  sup- 
posed that  this  mist  was  caused  by  the  presence  of  a  third  modifica- 
tion of  oxygen,  called  antozone,  which  was  supposed  to  be  pro- 
duced simultaneously  with  ozone  by  electrical  action,  and  by  pro- 
cesses of  oxidation.  Later  research  has,  however,  disproved  the 
existence  of  such  a  third  modification,  and  although  it  is  impossible 
at  present  to  account  for  all  the  effects  which  have  been  ascribed  to 
antozone,  in  many  cases  they  seem  to  be  due  to  the  presence  of  hydro- 
gen peroxide,  an  oxide  of  hydrogen  having  the  symbol  H2CX,. 


CHAPTEE   X. 
SULPHUR.  SELENIUM  AND  TELLURIUM. 

SULPHUR    (s). 

109.  Sulphur  occurs  somewhat  abundantly  in  nature  both  in 
the  free  state  and  in  combination  with  other  elements.  Many 
ores  of  metals,  for  example,  are  sulphur  compounds.  It  is  a 
component  of  several  abundant  salts,  such  as  the  sulphates  of 
calcium,  barium  and  sodium,  and  occurs  in  small  proportion  in 
many  animal  and  vegetable  substances.  Free  sulphur  is  found 


72  PROPERTIES  OF  SULPHUR.  [§  HO. 

chiefly  in  volcanic  districts.  Generally  it  occurs  mixed  with 
earthy  matters,  but  it  often  forms  distinct  veins,  and  is  some- 
times found  in  the  shape  of  well-defined  crystals  of  considerable 
size.  At  the  present  time  about  nine-tenths  of  the  sulphur  of 
commerce  comes  from  Sicily. 

Native  sulphur  is  usually  subjected  to  a  rough  purification  at  the 
place  of  its  occurrence.  This  purification  is  sometimes  effected  by 
distilling  the  volcanic  earth  in  retorts  or  jars  of  earthenware  ;  or,  if 
the  earth  be  very  rich  in  sulphur,  it  is  simply  heated  in  large  kettles 
and  the  melted  sulphur  dipped  off  from  above,  while  the  earthy  im- 
purities settle  to  the  bottom  of  the  kettle  :  sometimes  the  sulphur  is 
piled  up  in  heaps,  or  in  kilns,  and  set  on  fire,  a  portion  of  the  sulphur 
in  burning  furnishing  the  heat  by  which  the  rest  of  the  sulphur  is 
melted  :  the  melted  sulphur  flows  out  from  the  mass,  and  is  collected 
in  receivers.  As  the  crude  sulphur  comes  to  us,  it  is  in  irregular 
lumps  of  a  dirty  light-yellow  color,  and  is  largely  employed  for  manu- 
facturing purposes.  It  is  purified  by  being  distilled  from  iron  retorts 
into  large  chambers  constructed  of  masonry,  in  which  it  is  deposited 
either  in  the  form  ef  a  light  powder,  known  as  flowers  of  sulphur,  or 
in  the  liquid  state,  according  to  the  temperature  of  the  chambers. 

110.  At  the  ordinary  temperature  of  the  air,  sulphur  is  a 
brittle  solid   of  a  peculiar  light-yellow   color.     It   has  neither 
taste  nor  smell,  excepting  that  when  rubbed  it  exhales  a  faint 
and  peculiar  odor.     Most  of  the  odors  which  in  every-day  life 
are  referred  to  sulphur  are  really  the  odors  of  various  compounds 
of  sulphur,   and  are  not  evolved  by  the  element  itself.     The 
symbol  of  sulphur  is  S :  its  atomic  weight  is  32,  being  precisely 
twice  as  great  as  the  atomic  weight  of  oxygen. 

111.  Sulphur  behaves  in  a  very  remarkable  manner  on  being 
heated.     When  melted  at  the  lowest  possible  temperature,  100° 
to  115°,  it  forms  a  limpid  liquid  of  a  light-yellow  color  ;  but,  if 
this  liquid  be  heated  more  strongly,  it  begins  to  become  viscid 
and  dark-colored  at  about  150°,  and  at  170°  to  200°  it  is  almost 
black,  and  at  the  same  time  so  thick  and  tenacious  that  it  can 
not  be  poured  from  the  vessel  which  holds  it,  even  if  the  vessel 
be  inverted.     At  330°   to   340°  it  regains  its  fluidity  in  part, 
though  the  liquid  is   still  dark-colored,   and   finally,  at    about 


§  1 1 3.]  SOFT  StfLt>HUR.  -  CR  YSTALLIZA TlOtf.  73 

440°,  it  begins  to  boil,  and  is  converted  into  an  amber-colored 
vapor.  The  specific  gravity  of  sulphur  vapor,  referred  to  hydro- 
gen, is  32. 

112.  If  melted  sulphur  in  the  viscid  state,  or,  better,  that 
which  has  regained  its  mobility,  be  suddenly  cooled,  a  semi-solid 
modification  of  sulphur,  remarkably  different  from  the  ordinary 
form,  will  be  obtained. 

Exp.  44.  —  Place  in  a  test-tube,  of  about  30  c.  c.  capacity,  15  to 
20  grms.  of  coarsely-powdered  sulphur  ;  melt  Fig. 

the  sulphur  slowly  over  the  gas-lamp,  and 
continue  to  heat  it  until  it  begins  to  boil, 
noting,  meanwhile,  the  changes  which  the 
sulphur  undergoes, — as  described  in  §  111. 
Filially,  pour  the  hot  sulphur,  in  a  fine  stream, 
into  a  large  dish  full  of  cold  water.  There 
will  be  obtained  a  soft,  elastic,  reddish-brown 
mass,  which  can  be  kneaded  and  moulded 
like  wax,  and  drawn  out  into  threads  like 
caoutchouc. 

This  soft  sulphur  can  not  be  preserved  for  any  great  length  of 
time  ;  it  slowly  hardens  and  changes  into  ordinary  brittle  yellow 
sulphur. 

113.  Sulphur   may   readily    be    obtained    in    the   form   of 

'crystals. 

Exp.  45.  —  In  a  small  beaker  glass,  or  porcelain  capsule,  slowly 
heat  50  to  60  grms.  of  sulphur  until  it  has  entirely  melted.  Kemove 
•the  vessel  from  the  lamp,  and  allow  it  to  cool  slowly  until  about  a 
quarter  part  of  the  sulphur  has  solidified  ;  then  pour  off  into  a  basin 
of  water  that  portion  of  the  sulphur  which  is  still  liquid,  breaking 
through,  for  this  purpose,  the  crust  at  the  top  of  the  liquid,  if  any  such 
have  formed.  The  interior  of  the  vessel  will  be  found  to  be  lined 
with  transparent  crystals. 

Exp.  46.  —  In  a  test-tube,  melt  enough  sulphur  to  fill  one-quarter 
•of  the  tube  ;  place  the  tube  in  such  a  position  that  its  contents  may 
cool  slowly  and  quietly,  and  then  watch  the  formation  of  crystals  as 
they  shoot  out  from  the  comparatively  cold  walls  of  the  tube  towards 
the  centre  of  the  liquid. 
7 


74  SYSTEMS  OF  CRYSTALLIZATION.  [§  H4. 

Exp,  45  represents  one  general  method  of  obtaining  crystals. 
Crystals  of  many  of  the  metals,  lead  and  bismuth  for  example, 
can  be  obtained  in  a  similar  manner  :  it  is  only  necessary  to  per- 
form the  operation  in  a  crucible  of  some  refractory  material, 
placed  in  a  furnace. 

Exp.  46,  besides  illustrating  the  manner  in  which  crystals 
form,  teaches  us  something  of  the  physical  structure  of  solid 
bodies.  The  solid  mass  of  sulphur  which  is  left  in  the  test- 
tube,  when  it  has  become  cold,  is  evidently  nothing  more  than 
a  compact  bundle  of  interlaced  crystals  :  it  possesses  what  is 
called  a  crystalline  structure,  This  crystalline  structure  is 
apt  to  render  a  body  brittle  :  substances  which  possess  it  are 
liable  to  break  "  with  the  grain,"  or  to  split  in  certain  direc- 
tions determined  by  the  shape  of  the  crystals,  and  called  lines 
of  cleavage  :  a  stick  of  roll-brimstone,  for  example,  may  be 
readily  broken  or  cut  across,  but  not  so  easily  in  the  direction 
of  its  length. 

114.  Another  easy  way  to  crystallize  sulphur  is  by  the 
method  of  solution  and  evaporation,  such  as  was  employed  in 
the  preparation  of  potassium  nitrate  (Exp.  25).  Sulphur 
is  not  soluble  in  water,  but  it  dissolves  readily  in  a  liquid  com- 
pound of  sulphur  and  carbon,  known  as  carbon  bisulphide, 
which,  being  readily  volatile,  quickly  escapes,  on  exposure  to 
the  air,  and  so  deposits  the  sulphur.  The  crystals  thus  ob- 
tained differ  in  shape  from  those  obtained  by  the  method  of 
fusion. 

Although  thousands  of  crystal-forms  occur  in  nature  or  have  been 
produced  by  art,  it  has  been  found  possible  to  refer  these  forms  to  six 
general  classes  called  systems  of  crystallization.  It  is  true  of  almost 
all  chemical  substances  which  can  be  obtained  in  crystals,  that  while 
the  individual  crystals  may  vary  somewhat  in  form,  all  the  forms  in 
which  the  substance  occurs  are  such  as  may  be  referred  to  one  and  the 
same  system.  In  the  case  of  sulphur,  however,  the  crystals  obtained 
by  the  method  of  fusion,  and  those  obtained  by  the  method  of  solution, 
must  be  referred  to  two  entirely  distinct  systems.  There  are  other 
substances  besides  sulphur  which  present  this  same  phenomenon. 
Substances  which  are  thus  capable  of  assuming  crystalline  forms 


§  116.]  SULPHIDES.  75 

belonging  to  two  different  systems  are  said  to  be  dimorphous  (two- 
formed). 

The  two  varieties  of  sulphur  differ  considerably  in  various  physical 
properties.  One  variety  may,  however,  be  converted  into  the  other, 
and  their  chemical  composition  is  identical.  Each  is  sulphur,  and 
nothing  more.  The  amorphous  "  soft  sulphur  "  obtained  in  Exp.  44 
may  be  regarded  as  a  third  modification  of  sulphur. 

Crystals  of  sulphur  of  large  size  and  great  beauty  occur  in  Na- 
ture, and  are  supposed  to  have  been  formed  by  sublimation,  i.  e., 
the  sulphur  has  been  converted  into  vapor,  and  the  vapor  cooled 
very  slowly.  The  method  is  hardly  practicable  in  the  laboratory, 
although  crystals  have  been  formed  artificially  in  this  way. 

115.  Sulphur  unites  energetically  with  most  of  the  other 
elements,  such  union  being,  in  many  cases,  attended  with 
evolution  of  light.  Most  of  the  metals,  for  example,  combine 
with  it  directly,  just  as  they  do  with  oxygen. 

This  has  already  been  illustrated  in  the  case 
of  copper  by  Exp.  1,  §  2.  The  product  of  this 
reaction  was  copper  sulphide  ;  and,  in  general, 
compounds  of  sulphur  with  the  metallic  ele- 
ments are  called  sulphides. 

Exp.  47.  —  Mix  intimately  4  grins,  of 
flowers  of  sulphur  and  7  grms.  of  the  finest 
iron  filings.  Place  the  mixture  in  an  ignition- 
tube  10  to  12  c.  m.  long,  and  heat  the  lower 
end  of  the  tube  over  the  gas-lamp.  In  a  short 
time  the  mass  will  begin  to  glow,  as  the  sulphur 
and  iron  enter  into  chemical  combination,  and  . 
this  ignition  will,  of  itself,  pass  through  the  entire  length  of  the  tube, 
even  if  the  lamp  be  withdrawn.  The  final  product  of  the  reaction 
is  iron  sulphide. 

116.  Sulphur  unites  readily  with  oxygen  at  a  comparatively 
low  temperature.-  When  heated  in  the  air,  it  takes  fire  at  about 
250°,  and  burns  with  a  peculiar  blue  light.  The  irritating,  suf- 
focating gas,  which  is  produced,  will  be  shortly  described  under 
the  name  of  sulphurous  anhydride. 

The  use  of  sulphur  on  ordinary  matches  depends  on  the  low  tern- 


76  tiYVkOGEN  SVLPHtM.  [jj  \\^ 

perature  at  which  it  takes  fire.     Being  ignited  by  the  burning  phos- 
phorus, it  burns  until  the  less  readily  combustible  wood  is  set  on  fire. 

117.  Hydrogen  sulphide  (H2s)  or  sulphuretted  hydrogen,  as  it 
is  often  called,  is  a  colorless  gas  which  smells  like  rotten  eggs. 
It  may  be  conveniently  prepared  by  treating  iron  sulphide  with 
dilute  chlorhydric  acid. 

Exp.  48.  —  In  a  gas-bottle,  Fig.  26,  put  10  or  12  grms.  of  iron 
sulphide  (see  Exp.  47)  ;  replace  the  cork  in  the  bottle  and  introduce 
Fig.  26.  th&  gas  delivery-tube  into  another  small  bottle 

containing  cold  water,  letting  it  dip  5  or  6  c.  in. 
beneath  the  surface  of  the  water.  Through 
the  thistle-tube,  pour  into  the  gas-bottle  water 
enough  to  seal  the  lower  extremity  of  this 
tube  :  then  add,  through  the  thistle-tube  as  be- 
fore, 2  or  3  teaspoonfuls  of  strong  chlorhydric 
acid,  and  observe  that  bubbles  of  gas  soon  be- 
gin to  pass  through  the  water  in  the  absorption 
bottle. 

Hydrogen  sulphide  is  soluble  in  water  to  a 
considerable  extent,  and  is  consequently  taken 
up  by  the  water  in  the  absorption  bottle.  The 
solution  thus  obtained,  known  as  sulphuretted-hydrogen-water,  is 
much  employed  as  a  reagent  in  chemical  laboratories. 

When  the  disengagement  of  gas  slackens,  a  new  portion  of  chlor- 
hydric acid  may  be  added  through  the  thistle-tube,  and  this  process 
continued  until  the  water  in  the  absorption  bottle  smells  strongly  of 
the  gas. 

This  experiment  should  be  performed  out  of  doors,  or  in  a  draught 
of  air  so  arranged  that  those  portions  of  the  gas  which  escape  solution 
shall  be  carried  away  from  the  operator. 

The  reaction  which  takes  place  may  be  represented  as  follows  :  — 

FeS  -f  2HC1  ==  FeCl2  -f  H2S. 

118.  Hydrogen  sulphide  is  readily  inflammable.  It  burns 
with  a  blue  flame,  producing  water  and  sulphurous  acid  gas  :  — 
H2S  +  30  =  H20  +  S02. 

Exp.  49.  —  To  the  delivery-tube  of  the  gas-bottle  employed 
in  generating  hydrogen  sulphide,  attach  a  drying-tube  containing 


120.' 


HYDROGEN  SULPHIDE. 


77 


fragments  of  calcium  chloride,  and  with  the  tube  connect  a  piece 
of  No.  6  glass  tubing  drawn  out  to  a  fine  point.          Fis?. 
When   the   apparatus  is  full  of    the  gas,  apply  a 
match  to  the  end  of  the  tube.     The  gas  will  take 
fire,  and  burn  with  a  blue  flame.     If  a   dry  bot- 
tle be  held  over  the  flame,  the  walls  will  become 
coated  with  moisture  which  will  have  an  acid  reac- 
tion and  will  redden  blue  litmus  paper. 

The   jet   of  hydrogen    sulphide 
should  not  be  lighted  until  all  the 
air  is  expelled  from  the  apparatus,  as  this  gas  forms  an  explosive  mix- 
ture with  air. 

119.  Hydrogen  sulphide  is  readily  decomposed  by  heat,  as 
may  be  shown  by  passing  a  current  of  the  gas  through  a  glass 
tube,  heated  for  a  portion  of  its  length.  The  gas  will  be  separ- 
ated into  hydrogen  and  sulphur  :  the  latter  will  be  deposited 
on  tbe  cold  portion  of  the  tube. 

Analysis  has  proved  that  the  composition  of  hydrogen  sul- 
phide, both  by  volume  and  by  weight,  may  be  expressed  by  the 
following  diagram,  in  which  the  symbol  S  represents  a  unit 
volume  of  sulphur  in  the  state  of  vapor. 


120.  Hydrogen  sulphide  is  very  poisonous  :  when  respired  in 
the  pure  state,  it  quickly  proves  fatal,  and  it  is  very  deleterious, 
even  though  largely  diluted  with  atmospheric  air.  It  is  there 
fore  best,  when  experimenting  with  it,  to  operate  where  there  is 
a  free  circulation  of  air. 

The  gas  exists  as  a  natural  constituent  of  some  mineral  waters 
which  are  thence  called  sulphurous,  such  as  the  Virginia  Sulphur 
Springs,  and  the  mineral  springs  at  Sharon,  K  Y.  It  is  also 
found  in  the  air  and  water  of  foul  sewers,  and  wherever  animal 
matter  is  undergoing  putrefaction. 
7* 


78  COMPOUNDS  OF  SULPHUR  AND   OXYGEN.      [§121. 

121.  When  moist  hydrogen  sulphide  comes  in  contact  with 
certain  of  the  metals,  it  is  decomposed. 

Exp.  50. —  Place  a  drop  of  snlphuretted-hydrogen-water  (Exp.  48) 
upon  a  bright  piece  of  copper,  lead  or  silver.  The  metal  will  quickly 
become  black.  The  sulphur  of  the  hydrogen  sulphide  unites  with 
the  metal,  to  form  a  sulphide  of  the  metal,  while  the  hydrogen 
escapes,  or  we  may  say  that  the  metal  replaces  the  hydrogen  in  the 
hydrogen  sulphide. 

Cu  +  H2S  =  CuS    -f  2  H. 
2  Ag  -f-  H2S  =  Ag2S  -f  2  H. 

From  a  solution  of  any  compound  of  these  metals,  hydrogen 
sulphide  will  throw  down  the  sulphide  of  the  metal. 

Exp.  51.  —  Dissolve  a  small  crystal  of  lead  nitrate  in  a  test-tube 
half  full  of  water,  and  to  this  solution  add  a  few  drops  of  the  sulphur- 
etted-hydrogen-water. Lead  sulphide  is  thrown  down  as  a  black 
precipitate,  and  nitric  acid  is  set  free. 

PbN2O6  +  H2S  =  PbS  -j-  2  HNO8. 

On  account  of  this  property  of  precipitating  various  metallic 
sulphides,  hydrogen  sulphide  is  much  used  in  the  chemical 
laboratory  as  a  reagent. 

122.  Sulphur   and   Oxygen.  —  Of  the   compounds  of  sul- 
phur and  oxygen  the  most  important  are  sulphurous  anhydride 
and  sulphuric  anhydride. 

123.  Sulphurous    anhydride   (SO2),   commonly  called  sul- 
phurous acid  (see  §  63).  —  This  is  the  only  one  of  the  various 
compounds  of  oxygen  and  sulphur  which  can  be  formed  by  the 
direct  union  of  its  constituents.     It  is  produced  whenever  sul- 
phur is  burned  in  air  or  in  oxygen  gas. 

Fig.  28. 

Exp.  52. —  Light  a  piece  of  sulphur  in  a  deflagrating 
spoon,  and  suspend  the  latter  in  a  half-litre  bottle  full  of 
air.  On  examining  the  contents  of  the  bottle,  after  the 
sulphur  has  ceased  to  burn,  there  will  be  found  an  irritat- 
ing, suffocating  gas  having  the  peculiar  odor  which  is  famil- 
iar as  that  of  a  burning  match.  The  bottle  is  now  full  of 
sulphurous  anhydride,  mixed  with  the  nitrogen  originally 
present  in  the  air. 


§  125.]  PROPERTIES  OF  SULPHUROUS  ACID.  79 

An  easier  method  of  preparing  pure  sulphurous  acid  is  by 
depriving  common  sulphuric  acid  of  part  of  its  oxygen.*  This 
can  be  effected  by  a  variety  of  reducing  or  deoxidizing  agents. 
For  example,  when  concentrated  sulphuric  acid  is  heated  with 
metallic  copper,  there  is  formed  a  sulphate  of  the  metal,  water 
and  sulphurous  acid  :  — 

Cu  +  2  H,S04  =  CuS04  +  2  H2O  -f  SO2. 

Certain  other  metals,  such  as  mercury,  for  example,  can  be  employed 
instead  of  copper,  the  reaction  being  precisely  similar. 

124.  Sulphurous  acid  is  a  transparent  and  colorless  gas.     It 
is  irrespirable  and  suffocating,  and  when  mixed  with  air,  even  in 
small  proportion,  occasions  violent  coughing.     It  is  not  inflam- 
mable, but,  on  the  contrary,  it  stops  combustion. 

The  flame  of  a  taper  is  immediately  extinguished  on  being  immersed 
in  sulphurous  acid  gas,  just  as  it  is  by  nitrogen.  A  useful  application 
of  this  property  of  the  gas  is  in  extinguishing  burning  chimneys.  A 
handful  of  fragments  of  sulphur  being  thrown  upon  the  hot  coals  in 
the  grate,  and  the  openings  of  the  fireplace  being  closed  in  such  man- 
ner that  no  air  shall  enter  the  chimney,  excepting  that  which  passes 
through  the  fire,  the  chimney  will  quickly  become  filled  with  an 
atmosphere  of  sulphurous  acid  mixed  with  nitrogen  from  the  air  em- 
ployed in  burning  the  sulphur,  and  the  burning  soot  upon  the  walls 
of  the  chimney  will  be  immediately  extinguished. 

It  is,  of  course,  essential  that  the  chimney  should  then  be  closed  at 
the  top,  so  that  air  may  be  excluded  and  the  chimney  kept  full  of  the 
fire- extinguishing  atmosphere  until  its  walls  shall  have  cooled  to  below 
the  kindling  temperature  of  the  soot. 

125.  Sulphurous  anhydride  can  readily  be  obtained  in  the 
liquid  state  by  passing  the  gas  through  a  U-tube  immersed  in  a 
freezing-mixture  of  ice  and  salt.     On  being  exposed  to  the  air  at 
ordinary  temperatures,  this  liquid  evaporates  with  great  rapidity, 
and  consequently  occasions  very  intense  cold. 

*  The  substances  now  designated  as  anhydrides  were  formerly  called  acids,  as 
stated  in  §  63.  In  the  case  of  sulphurous,  arsenious  and  carbonic  anhydrides,  the 
popular  names  sulphurous,  arsenious  and  carbonic  acids  have  such  currency  that 
they  will  be  employed  in  this  Manual  where  no  ambiguity  can  arise  from  such  use. 


80  SULPHUROUS  ACID  BLEACHES.  [§  126. 

If  a  quantity  of  the  liquid  be  poured  into  water,  the  temperature 
of  which  is  a  few  degrees  above  0°,  a  portion  will  evaporate  at  once, 
another  portion  will  dissolve  in  the  water  and  a  third  portion  of  the 
heavy  oily  liquid  will  sink  to  the  bottom  of  the  vessel.  If  the  por- 
tion which  has  thus  subsided  be  stirred  with  a  glass  rod,  it  will  boil 
at  once,  and  the  temperature  of  the  water  will  be  so  much  reduced 
that  a  portion,  or  even  the  whole,  of  the  water  will  be  frozen. 

The  volumetric  composition  of  sulphurous  anhydride  is  1 
volume  of  sulphur  vapor  and  2  volumes  of  oxygen  condensed  to 
2  volumes  of  the  compound  gas.  The  gas  is  very  readily  soluble 
in  water,  and  may  be  regarded  as  combining  with  a  portion  of 
the  water  to  form  sulphurous  acid,  the  formula  of  which  would 
be  H2SO3.  The  term  "  sulphurous  acid  "  is,  however,  ordinarily 
used  to  denote  the  gas  SO2. 

126.  An  important  property  of  sulphurous  acid  is  its  power 
of  bleaching  vegetable  colors.  It  is  extensively  employed  in 
bleaching  articles  of  straw,  wool,  silk,  etc.,  which  would  be 
injured  by  chlorine.  The  bleaching  may  be  effected  by  immer- 
sion in  the  aqueous  solution  of  sulphurous  acid  or  by  exposure 
to  the  fumes  of  burning  sulphur.  In  the  latter  case  the  articles 
to  be  bleached  must  be  moistened.  The  dry  anhydride  does  not 
bleach.  In  most  cases  sulphurous  acid  does  not  destroy  the 
coloring  matters  as  chlorine  does,  but  seems  to  combine  with 
them  to  form  colorless  compounds.  These  colorless  compounds 
can  be  broken  up,  with  restoration  of  color,  by  exposing  them 
to  the  action  of  various  chemical  agents  capable  of  setting  free 
sulphurous  acid. 

Exp.  53.  —  Bleach  a  red  rose  by  hanging  it  in  a  bottle  in  which 
sulphur  has  been  burned,  or  by  holding  it  over  burning  sulphur.  Im- 
merse the  bleached  rose  in  dilute  sulphuric  acid,  dry  and  warm  it, 
and  observe  that  the  color  will  re-appear. 

In  the  arts,  the  process  of  bleaching  is  usually  conducted  in  large 
chambers,  in  which  the  slightly  moistened  articles  are  hung  while  sul- 
phur is  burned  below.  The  damp  goods  absorb  the  gas  and  gradually 
become  white.  A  practical  illustration  of  the  restoration  of  color  by 
chemical  agents  is  seen  in  the  reproduction  of  the  original  yellow 
color  of  the  wool  when  new  flannel  is  washed.  The  alkali  of  the 
soap  removes  the  sulphurous  acid,  and  the  color  re-appears. 


§129.]  ^  SULPHURIC  ACID.  81 

127.  Sulphuric  anhydride  (SO,)  may  be  prepared  by  the 
direct  oxidation  of  sulphurous  anhydride.     If  a  mixture  of 
sulphurous  anhydride  and  oxygen  be  passed  over  heated,  very 
finely  divided  platinum  (platinum  sponge),  the  two  gases  unite 
to  form  sulphuric  anhydride,  which  condenses  in  the  cooled 
receiver.      It   is  a  white,  waxlike  solid,   crystallizing  in  silky 
libres,  resembling  asbestos.     If  a  bit  of  it  be  thrown  into  water, 
the  water  hisses  as  if  a  hot  iron  had  been  thrust  into  it ;  and 
the  sulphuric  anhydride  unites  with  a  portion  of  the  water  with 
the  evolution  of  great  heat  to  form  sulphuric  acid.     The  solid 
anhydride  has  so  great  an  attraction  for  water,  that  it  can  be 
preserved  only  in  dry  tubes  sealed  at  the  lamp. 

128.  Sulphuric  acid  (H2SO4)  is  one  of  the  most  important 
products  of  chemical  manufacture,   and  is  made  in  enormous 
quantities.     In  the  same  way  that  the  metal  iron  may  be  said  to 
be  the  basis  of  all  mechanical  industries,  sulphuric  acid  lies  at 
the  foundation  of  the  chemical  arts.     By  means  of  sulphuric 
acid,  the  chemist  either  directly  or  indirectly  prepares  almost 
every  thing  with  which  he  has  commonly  to  deal. 

129.  Sulphuric  acid  is  made  by  oxidizing  sulphurous  acid. 
This  oxidation  cannot   be  effected   directly  in   any  economical 
manner ;  it  is  necessary  to  use  some  oxidizing  agent. 

This  term  oxidizing  agent  is  applied  to  a  substance  which  habit- 
ually and  readily  imparts  oxygen  to  other  bodies  with  which  it  is 
brought  in  contact :  on  the  other  hand,  a  substance  which  habitually 
and  readily  takes  oxygen  out  of  other  substances  with  which  it  is 
brought  in  contact  is  called  a  reducing  agent.*  Nitric  acid,  such  as 
was  prepared  in  Exp.  22,  §  59,  is  a  very  powerful  oxidizing  agent,' 
and  sulphuric  acid  might  be  made  by  boiling  sulphur  for  a  long  time 
in  nitric  acid.  This  method  would,  however,  not  be  practicable  on  a 
large  scale.  Nitric  acid  also  oxidizes  sulphurous  acid. 

Exp.  54. — Charge  a  bottle,  of  the  capacity  of  a  litre  or  more,  with 
sulphurous  acid  by  burning  in  it  a  bit  of  sulphur.  Fasten  a  shaving, 
or,  better,  a  tuft  of  gun-cotton,  upon  a  glass  rod  or  tube  bent  at  one 
end  in  the  form  of  a  hook  ;  wet  the  shaving  in  concentrated  nitric 
acid,  and  hang  it  in  the  bottle  of  sulphurous  acid.  Red  fumes  of 

*  The  terms  oxidizing  agent  and  reducing  agent  are  often  employed  in  a  much 
wider  sense  than  here  implied.  See  page  290. 


82  MANUFACTURE  OF  SULPHURIC  ACID.  [§  13Q. 

nitrogen  peroxide  will  immediately  form  about  the  nitric  acid,  and 
will  gradually  fill  the  bottle.  The  appearance  of  the  red  fumes 
(nitrogen  peroxide)  shows  that  there  has  been  a  loss  of  oxygen  on  the 
part  of  the  nitric  acid.  The  reaction  may  be  thus  written  :  — 

2  HNO3  -f  SO2  =  H2SO4  -f  2  NO2. 

In  this  case  sulphurous  acid  is  an  example  of  a  reducing  agent.  Sul- 
phurous acid  in  the  presence  of  much  moisture  can  take  oxygen  from 
all  the  higher  oxides  (and  acids)  of  nitrogen,  as  HNO2,  NO2,  and 
HNO3,  and  reduce  them  all  to  nitric  oxide,  NO. 

130.  The  method  employed  in  the  actual  preparation  of  sul- 
phuric acid  upon  the  large  scale  depends  upon  the  fact  illus- 
trated in  the  last  experiment. 

Fig.  39. 


Fig.  29  shows,  in  a  rough  and  very  general  way,  the  manner  in 
which  the  manufacture  is  conducted.  The  sulphurous  acid  is  obtained 
by  burning  crude  sulphur  or,  more  commonly,  a  compound  of  sulphur 
and  iron,  known  as  iron  pyrites,  in  properly-constructed  furnaces. 
The  gas,  together  with  a  large  excess  of  atmospheric  air,  is  then  con- 
ducted into  the  first  of  a  series  of  enormous  chambers,  into  which  jets 
of  steam  are  constantly  blowing  :  these  chambers  are  constructed  of 
sheet-lead,  a  metal  on  which  cold  sulphuric  acid  has  little  action. 
Nitrous  fumes  are  supplied  either  by  allowing  nitric  acid  to  fall  in 
fine  streams  through  the  incoming  current  of  sulphurous  acid  and 
air,  or  from  the  decomposition  of  sodium  nitrate  by  means  of  sulphuric 
acid,  this  decomposition  taking  place  in  an  iron  pot  heated  by  the 
burning  sulphur. 

In  conformity  with  the  principles  above  stated,  the  SO2  in  contact 
with  the  steam,  reacts  upon  the  nitrous  fumes  :  there  is  formed  sulphuric 


§  132.]  FORMATION  OF  SULPHURIC  ACID.  83 

acid,  which  condenses  upon  the  sides  of  the  chamber  and  trickles 
down  to  the  floor,  and  nitric  oxide.  But,  as  there  is  present  in  the 
chamber  an  excess  of  air,  the  NO  immediately  unites  with  a  portion 
of  the  oxygen  therein  contained,  and  is  converted  into  NO2.  This 
NO2  immediately  reacts  upon  a  new  portion  of  SO2,  and  the  process 
thus  goes  on  through  a  whole  series  of  leaden  chambers,  the  very 
small  portion  of  nitric  acid  at  first  taken  being  sufficient  to  prepare  a 
large  quantity  of  sulphuric  acid.  In  reality,  the  oxygen  emploved  in 
converting  the  sulphurous  into  sulphuric  acid  all  comes  from  the  air, 
excepting  a  very  little  at  first  :  the  nitrous  fumes  serve  only  as  a  con- 
veyer of  oxygen.  The  NO  takes  oxygen  from  the  air  and  transfers 
it  to  the  sulphurous  acid,  which  is,  by  itself  and  unaided,  incapable 
of  combining  with  oxygen.  It  will,  of  course,  be  understood,  that 
although  we  trace  out  these  reactions  as  if  they  were  consecutive, 
they  are  really,  so  far  as  we  know,  simultaneous. 

Theoretically,  a  single  portion  of  nitric  acid  would  be  sufficient  to 
effect  the  conversion  of  an  unlimited  amount  of  sulphurous  into  sul- 
phuric acid,  but  practically  this  power  is  qualified  by  a  variety  of  cir- 
cumstances. It  is  found  to  be  impossible,  for  example,  to  introduce 
new  portions  of  air  into  the  mixture  of  sulphurous  acid  and  nitric 
oxide  for  an  indefinite  period  ;  for,  at  a  certain  point,  these  gases 
become  so  loaded  down  with  nitrogen  derived  from  the  air  already 
consumed,  that  they  are  as  good  as  lost  in  it.  In  general,  the  flow 
of  gases  is  so  regulated  that  all  the  sulphurous  acid  shall  be  oxidized, 
and  that  nothing  but  nitric  oxide  and  the  waste  nitrogen  shall  pass 
out  of  the  last  leaden  chamber. 

131.  The  acid  obtained  in  the  lead  chambers  as  described 
above  is  very  dilute.     It  is  concentrated  by  evaporating  it,  first 
in  leaden  pans,  and  finally  in  large  glass  retorts  or  in  platinum 
stills,  until  it  has  nearly  the  composition  H2SO4. 

The  acid  thus  boiled  down  is  the  concentrated  sulphuric  acid, 
or  oil  of  vitriol,  of  commerce  ;  its  specific  gravity  is  usually 
about  1.83,  that  of  the  absolutely  pure  acid  being  1.842.  Be- 
sides this  slight  excess  of  water,  it  contains  also,  in  solution,  a 
certain  quantity  of  lead  sulphate,  and  a  variety  of  other  impuri- 
ties. For  most  purposes,  however,  it  will  answer  as  well  as  the 
pure  acid.  Like  the  latter,  it  is  a  heavy,  oily,  colorless  and 
odorless  liquid,  boiling  at  about  330°. 

132.  At  the  ordinary  temperature,  sulphuric   acid  does  not 


84  PROPERTIES  OF  SULPHURIC  ACID.  [§  133. 

vaporize,  but,  on  the  contrary,  greedily  absorbs  water  from  the 
air,  and  so  increases  in  bulk.  In  moist  weather,  its  bulk  may 
increase  to  the  extent  of  a  quarter  or  more,  in  the  course  of  a 
single  day,  and,  by  longer  exposure,  a  still  larger  quantity  of 
water  will  be  taken  up  ;  the  acid  must  always  be  kept,  there- 
fore, in  tightly-stoppered  bottles. 

Sulphuric  acid  unites  with  liquid  water,  with  great  energy, 
much  heat  being  evolved  at  the  moment  of  combination  :  dur- 
ing the  union  a  certain  amount  of  condensation  occurs,  the 
mixture,  when  cold,  occupying  less  space  than  was  previously 
occupied  by  the  acid  and  the  water.  The  water  and  acid  may 
be  mixed  in  all  proportions,  being  mutually  soluble  one  in  the 
other. 

In  mixing  water  and  sulphuric  acid,  the  acid  should  always  be 
poured  into  the  water,  in  a  fine  stream,  not  the  water  into  the  acid,  — 
the  water  being  meanwhile  stirred.  In  this  way  the  heavy  acid  has 
an  opportunity  to  mix  with  the  water  as  it  sinks  down  through  it. 
If,  by  any  accident,  water  were  to  fall  upon  sulphuric  acid,  it  would 
float  on  top  of  it,  and  great  heat  would  be  developed  at  the  point  of 
contact  of  the  two  liquids  :  if  the  quantities  of  acid  and  water  were 
large,  sudden  bursts  of  steam  would  be  occasioned,  and  serious  damage 
might  arise  from  the  scattering  about  of  portions  of  the  acid. 

Exp.  55.  —  Place  in  a  beaker  glass  of  about  250  c.  c.  capacity, 
30  c.  c.  of  water  ;  in  accordance  with  the  directions  above  given,  pour 
into  the  water  120  grms.  of  concentrated  sulphuric  acid,  and  stir  the 
mixture  with  a  narrow  test-tube  containing  a  teaspoonful  of  water. 
So  much  heat  will  be  evolved  during  the  union  of  the  water  and  the 
acid  that  the  water  in  the  test-tube  will  boil. 

133.  Sulphuric  acid  is  one  of  the  most  powerful  acids 
known.  When  diluted  with  a  thousand  times  its  bulk  of 
water,  it  is  still  capable  of  reddening  blue  litmus.  It  sets  free 
most  of  the  other  acids  from  their  salts,  in  the  same  way  that 
we  have  seen  it  set  free  nitric  acid  from  sodium  nitrate  in 
Exp.  22,  §  59.  It  is  intensely  caustic  and  corrosive,  and 
quickly  chars  and  destroys  most  vegetable  and  animal  sub- 
stances. 

Exp.  56.  — Into  a  test-glass  pour  a  table-spoonful  of  sulphuric 


§  136.]      SULPHATES.  —  FUMISG  SULPHURIC  ACID.  85 

acid  ?.nd  immerse  in  it  a  splinter  of  wood.  The  wood  will  blacken 
as  if  charred  by  fire,  and  the  acid  will  become  dark-colored.  Wood 
is  composed  of  carbon,  hydrogen  and  oxygen,  and  since  sulphuric 
acid  unites  with  compounds  of  hydrogen  and  oxygen,  rather  than 
with  carbon,  a  portion  of  the  latter  is  left  free  ;  some  carbonaceous 
matter  is,  however,  dissolved  by  the  acid  and  darkens  it.  The  acid 
of  commerce  is  often  dark-colored  from  fragments  of  straw  or  other 
organic  matter  having  accidentally  fallen  into  it. 

134.  Sulphates.  —  If    the   hydrogen   of    sulphuric   acid  be 
replaced  by  various  metals,  a  class  of  bodies  is  formed  called 
sulphates :  thus,  Na2SO4  is  sodium  sulphate  \  CaSO4  is  calcium 
sulphate,  etc. 

In  the  formation  of  the  sulphates  of  those  metals  which  replace 
hydrogen  atom  for  atom  (§  74),  it  is  not  necessary  that  both  atoms  of 
hydrogen  in  the  sulphuric  acid,  H2SO4,  should  be  replaced.  We 
may,  for  example,  have  a  compound  in  which  sodium  replaces  only 
one  of  the  hydrogen  atoms  ;  namely,  HNaSO4,  hydrogen  sodium 
sulphate.  Acids  like  sulphuric  acid,  which  have  two  replaceable  hy- 
drogen atoms,  are  called  bi-basic. 

135.  Fuming   Sulphuric   Acid,  —  Sulphuric   acid   was   for- 
merly made  by  distilling  in  earthen  retorts  the  salt  now  known 
as  ferrous  sulphate,  formerly  called  green  vitriol.      Hence  the 
origin  of  the  name  oil  of  vitriol,  which,  in  England  and  this 
country,  ha.s  come  to  be  applied  solely  to  the  common  acid, 
H2SO4.     The  acid  thus  obtained  is  a  dense  fuming  liquid,  which 
may  be  regarded  as  sulphuric  anhydride  dissolved  in  sulphuric 
acid.      It  is  used  principally  for  dissolving  indigo,   a   certain 
quantity  being  still  made  for  this  purpose. 

There  are  other  well-defined  compounds  of  oxygen  and  sul-. 
phur.     They,  are,  however,  of  much  less  importance,  and  are  of 
little  interest  in  an  elementary  manual. 

SELENIUM    (ge)    AND    TELLURIUM    (ie). 

136.  These  elements  are  rare,  and  of  little  or  no  industrial  impor- 
tance ;  but  to  the  chemist  they  are  exceedingly  interesting  on  account 
of  the  close  resemblance  they  bear  to  sulphur.     The  three  elements 
sulphur,  selenium  and  tellurium,  constitute  a  group  which  is  equally 


86  SELENIUM  AND   TELLURIUM.  [§  137, 

remarkable  with  that  formed  by  chlorine,  bromine  and  iodine.     (See 
§97.) 

137.  Selenium  is  never  found  in  any  considerable  quantity  in 
any  one  place.     Traces  of  it  occur  in  many  varieties  of  native  sulphur 
and  in  various  metallic  sulphides.     In  its  properties  and  in  its  chemi- 
cal behavior,  selenium  resembles  sulphur  in  many  respects,  while,  in 
others,  it  is  like  tellurium.     Like  sulphur  and  oxygen,  it  occurs  in 
distinct  allotropic  modifications  (§§  101,  114)  :   it  forms  with  hy- 
drogen a  compound,  hydrogen  selenide  (H2Se),  resembling  hydrogen 
sulphide  :  it  forms  an  acid,  selenic  acid  (H2SeO4),  resembling  sul- 
phuric acid.     There  are  selenates  possessing  characters  similar  to  the 
sulphates,  and  crystallizing  in  the  same  form  ;  and,  according  to  a 
principle  illustrated  by  the  chlorine  group,  selenium,  which  has  the 
higher  atomic  weight  (79.5),  is  a  weaker  chemical  agent  than  sulphur 
(32). 

138.  Tellurium  occurs  in  nature  even  more  rarely  than  selenium  ; 
sometimes  it  is  found  in  the  free  state,  but  more  generally  in  combina- 
tion with  the  heavy  metals,  such  as  gold,  silver,  lead,  copper  and 
bismuth.     Tellurium  is  of  a  silver- white  color  and  glittering  metallic 
lustre.     In  many  of  its  physical  characters  it  would  seem  to  be  allied 
to  certain  metals,  but  its  chemical  properties  place  it  in  the  same 
group  with  sulphur  and  selenium.  It  forms  compounds  with  hydrogen, 
oxygen  and  with  other  elements  which  resemble  the  corresponding 
sulphur  compounds.     Its  atomic  weight  is  128. 

The  elements  sulphur,  selenium  and  tellurium  in  their  chemical 
properties  are  closely  allied  to  oxygen.  Attention  has  already  been 
called  to  the  resemblance  of  the  compounds  of  selenium  and  tellurium 
to  those  of  sulphur.  The  formulae  of  a  few  of  these  compounds  are 
here  given  to  bring  the  matter  more  clearly  before  the  eye. 


Water.          Hydrogen  sulphide. 
H20                  H2S 

Hydrogen  selenide. 

H2Se 

Hydrogen  telluride. 

H2Te 

Iron  oxide.          Iron  sulphide. 

FeO                FeS 

Iron  selenide. 

FeSe 

Iron  telluride. 

FeTe 

Ether 
(Ethyl  oxide).         Ethyl  sulphide. 
(C2H5)2O             (C2H5XS 

Ethyl  selenide. 

(C2H5)2Se 

Ethyl  telluride. 

(C2H5)2Te 

Alcohol             Mercaptan  (Ethyl 
i  Ethyl  hydrate).     Hydrogen  sulphide). 

Selenium 
mercaptan. 

Tellurium 
inerpaptan. 

(C2H5)HO  (C2H5)HS  (C2H5)HSe  (C2H5)HTe 


§  139.]  COMBINATION  BY   VOLUME.  87 

CHAPTER  XL 
COMBINATION  BY  VOLUME. 

1 39.  A  comparison  of  the  formulae  representing  the  volumet- 
ric composition  of  all  the  well-defined  compound  gases  and 
vapors  which  have  been  thus  far  studied,  will  bring  into  clear 
view  some  of  the  general  facts  relating  to  combination  by 
volume. 

It  has  been  established,  by  experiment,  that  the  following 
compounds  are  formed  by  the  chemical  union,  without  conden- 
sation, of  equal  volumes  of  the  two  elements  which  enter  into 
each  compound  :  — 


Hydrogen 
1  vol. 

+ 

Chlorine 
1  vol. 

Chlorhydric  Acid 
2  vols. 

,  or 

H 

1 

4- 

Cl 

35.5 

HC1 

"  36.5 

Hydrogen 
1  vol. 

4- 

Bromine 
1  vol. 

Bromhydric  Acid 

2  vols. 

,  or 

H 

+ 

Br 

80 

HBr 

'  81 

Hydrogen 
1  vol. 

4- 

Iodine 
1  vol. 

lodohydric  Acid 
2  vols. 

,  or 

H 
1 

4- 

I 
127 

HI 

~  128 

Nitrogen 
1  vol. 

4- 

Oxygen 
1  vol. 

Nitric  oxide 
2  vols. 

,  or 

N 

14 

4- 

O 

16 

NO 

'  30 

It  has  further  been  found  that  the  following  compounds  of 
two  elements  contain  two  volumes  of  one  element  and  one 
volume  of  the  other,  but  that  these  three  volumes  are  condensed 
during  the  act  of  combination  into  two  volumes  :  — 


Hydrogen 
2  vols. 

+ 

Oxygen 
1  vol. 

Steam 
2  vols. 

i  or 

H2 

2 

4- 

0 

16 

_H20 

'    18 

Hydrogen 
2  vols. 

4- 

Sulphur 
1  vol. 

Hydrogen  Sulphide 
2  vols. 

,  or 

H2 

2 

4- 

a 

32 

_  H2S 

34 

Nitrogen 
2  vols. 

4- 

Oxygen 
1  vol. 

Nitrogen  Protoxide 
2  vols. 

,  or 

N2 

28 

4- 

0 

16 

_N20 

44 

Nitrogen 
1  vol. 

4- 

Oxygen 
2  vols. 

Nitrogen  Peroxide 
2  vols. 

,  or 

N 

14 

4- 

02 

32 

NO, 

"    46 

Sulphur 
1  vol. 

4- 

Oxygen 
2  vols. 

Sulphurous  Anhy- 
dride 2  vols. 

,  or 

B 

32 

+ 

o, 

32 

_  so, 

-     64 

To  this  list  must  be  added  hydrogen  selenide  (H2Se),  hydro- 
gen telluride  (H2Te),  selenious  anhydride  (SeO2)  and  tellurous 
anhydride  (TeO2). 


88  PRODUCT-VOLUME..  [§  HO. 

Lastly,  still  a  third  mode  of  combination  by  volume  with 
condensation  of  four  volumes  to  two  occurs  in  the  two  following 
cases  :  — 

Nitrogen         Hydrogen   _  Ammonia  N  H3  NH 

1  vol.  3  vols.  2  vols.  '        14  3  17 

Sulphur      .    Oxygen         _    Sulphuric  Anhy-          S  O3  SO3 

1  vol.  3  vols.  dride  2  vols.       '  °r  32    "        48  80 

In  all  these  cases,  the  unit-volume  is,  of  course,  the  same 
for  every  element  and  compound ;  what  the  absolute  bulk  of 
this  unit-volume  may  be,  is  not  an  essential  point,  for  the  rela- 
tions remain  the  same,  whatever  the  unit  of  measure.  Three 
condensation-ratios  are  thus  exhibited  :  first,  a  condensation 
of  0 ;  second,  one  of  J ;  and  third,  one  of  J.  The  space  occu- 
pied by  the  compound  molecule  is,  in  each  case,  exactly  twice 
the  unit-volume. 

The  examples  just  given,  although  including  all  the  com- 
pounds which  we  have  yet  studied,  are  only  very  few  compared 
with  the  vast  number  of  gaseous  compounds  which  have  been 
investigated,  and  where  the  same  thing  has  been  found  to  hold 
true.  Two  volumes  of  a  compound  gas  invariably  result 
from  the  chemical  combination  of  one  volume  of  hydrogen  with 
one  volume  of  chlorine,  of  two  volumes  of  hydrogen  with  one 
volume  of  oxygen,  of  three  volumes  of  hydrogen  with  one  vol- 
ume of  nitrogen,  and  so  on.  This  doubled  volume  is  often 
called  the  normal  or  product-volume  of  a  compound  gas. 
•  If,  in  considering  the  compounds  already  mentioned  in  this 
chapter,  we  choose  for  our  unit-volume  the  space  occupied  by 
the  atom  of  hydrogen  in  the  molecule  of  chlorhydric  acid  (i.  e., 
in  other  words,  the  volume  of  the  atom  of  hydrogen  when  not 
under  condensation),  we  shall  be  led  to  very  important  theoret- 
ical results.  For  then  our  product  volume  will  be  in  each  case 
the  space  occupied  by  the  molecule  of  the  compound  gas,  and 
we  shall  be  led  to  the  conclusion  that  the  space  occupied  by  a 
single  molecule  of  each  of  these  gaseous  compounds  is  the  same. 
This  is,  indeed,  believed  to  be  true  in  the  case  of  all  gaseous 
molecules.  In  organic  chemistry  a  great  multitude  of  com- 


§  !40.  THE  ELEMENTARY  OASES.  89 

pounds,  many  of  them  very  complicated,  have  been  investigated, 
and  the  same  law  has  been  found  to  hold  good.  The  molecule 
of  every  compound  in  the  gaseous  state  occupies  a  volume  twice 
as  large  as  that  occupied  by  the  atom  of  hydrogen. 

Since,  then,  the  molecule  of  a  compound  gas  or  vapor  occupies 
two  of  these  unit  volumes,  and  the  specific  gravity  of  a  gas  or 
vapor  is  the  weight  of  one  unit-volume  of  that  gas  or  vapor  as 
compared  with  the  weight  of  the  same  volume  of  hydrogen,  it  is 
obvious  that  the  specific  gravity  of  the  gas  or  vapor  may  be  found 
from  the  molecular  weight  by  dividing  the  latter  by  two.  The 
specific  gravity  of  a  compound  gas  or  vapor  is,  therefore,  one-half 
its  molecular  weight. 

140.  Molecular  condition  of  elementary  gases.— There  are 
certain  physical  laws  in  regard  to  compressibility  and  expansion  which 
govern  all  gases,  and  which  are  best  explained  by  the  hypothesis, 
usually  spoken  of  as  the  Law  of  Ampere, — that  equal  volumes  of  all 
gases,  simple  as  well  as  compound,  under  like  conditions  of  temperature 
and  pressure,  contain  the  same  number  of  molecules.  Starting  with  this 
hypothesis,  let  us  inquire  what  inferences  we  can  draw  with  regard  to 
the  molecular  condition  of  the  elementary  gases  when  in  the  free  state. 
Suppose,  then,  we  take  any  volume  of  hydrogen,  the  volume  occupied 
by  1000  molecules,  for  example  :  an  equal  volume  of  chlorine  will 
contain  the  same  number  of  molecules.  If  the  two  gases  be  mixed  and 
exposed  to  diffused  sunlight  they  will  combine  without  condensation 
to  form  chlorhydric  acid.  We  shall  then  have  two  volumes  of  chlor- 
hydric  acid.  According  to  the  assumption  just  made  that  equal  vol- 
umes of  all  gases  contain  the  same  number  of  molecules,  each  of  these 
two  volumes  will  contain  1000  molecules  of  the  acid  and  the  two 
volumes  will  contain  2000  molecules.  Each  molecule  of  the  acid 
contains  one  atom  of  hydrogen  and  one  atom  of  chlorine,  hence  in  the 
two  volumes  of  chlorhydric  acid  we  shall  have  2000  atoms  of  hydro- 
gen and  2000  atoms  of  chlorine.  These  2000  atoms  of  hydrogen  (or 
chlorine)  came  from  the  one  volume  of  the  gas  which  we  supposed  to 
contain  1000  molecules  ;  therefore,  this  volume  contained  at  the  same 
time  1000  molecules  and  2000  atoms  :  hence  each  molecule  must  be 
made  up  of  two  atoms.  It  is  clear  that  this  train  of  reasoning  is  in- 
dependent of  the  particular  numerical  value  assumed  as  the  number 
of  molecules  in  the  two  volumes  of  chlorhydric  acid.  If,  therefore. 


90  MOLECULAR  CONDITION  Off  [§  140. 

the  molecule  of  chlorhydric  acid  is  represented  by  tlie  formula  HC1, 
and  the  diagram,  — 


Cl 


there  is  good  reason  to  assign  to  free  hydrogen  and  free  chlorine  the 
formulae  HH  and  C1C1,  or  (H2  and  C12),  and  to  represent  the  con- 
stitution of  all  uncombined  gases  by  such  diagrams  as 


Cl 


Cl 

= 

C1C1 

Upon  these  models  the  molecular  formulae  of  most  of  the  elements 
with  which  we  have  become  acquainted  might  readily  be  written.  It 
is  only  in  a  free  state  that  the  elementary  gases  and  vapors  are  thus 
conceived  to  exist  as  molecules  ;  when  they  enter  into  combination,  it 
is  by  atoms  rather  than  by  molecules.  An  atom  of  hydrogen  unites 
with  an  atom  of  chlorine  :  three  atoms  of  hydrogen  combine  with  one 
of  nitrogen. 

We  may  study  the  molecular  condition  of  the  elementary  gases 
from  another  point  of  view.  If  the  Law  of  Ampere  be,  as  it  is  be- 
lieved to  be,  true  of  simple  as  well  as  of  compound  gases,  it  will  be 
true  that  the  vapor  density  (or  the  specific  gravity  of  the  sub- 
stance in  the  state  of  gas)  is  one-half  the  molecular  weight,  and, 
vice  versa,  that  the  molecular  weight  is  twice  the  vapor  density.  If, 
now,  the  specific  gravity  of  hydrogen  be  one,  its  molecular  weight 
must  be  2  x  1  =  2.  If  the  molecule  weigh  2  and  the  atom  weigh 
1,  the  unit  of  weight  being  the  same  in  both  cases,  the  molecule 
must  contain  2  atoms.  The  same  reasoning  will  hold  in  the  case  of 
the  elementary  gases,  oxygen,  chlorine,  and  nitrogen,  also  in  the  case 
of  the  elementary  substances,  bromine,  iodine,  sulphur,  selenium, 
tellurium,  sodium  and  potassium,  which  are  not  gases  under  ordinary 
atmospheric  conditions,  but  which  can  be  converted  into  gases  at  a 
higher  temperature.  As,  for  example, 


Vapor  Density. 

Moiec.  weigni 
=  V.  D.  x  2. 

Atomic  Wt.    J 

LMO.  oi  atoms 
Molecule. 

16 

32 

16 

2 

35.5 

71 

35.5 

2 

127 

254 

127 

2 

32 

64 

32 

2 

140.]  THE  ELEMENTARY  OASES.  01 


O 

Cl 

I 

3 

etc. 

Of  all  the  other  elementary  substances,  four,  namely,  arsenic, 
phosphorus,  mercury  arid  cadmium,  have  been  converted  into  vapor, 
and  the  specific  gravity  of  their  vapors  determined.  If  we  apply  the 
same  reasoning  to  them  we  find  that  the  molecules  of  arsenic  and 
phosphorus  contain  each  four  atoms,  while  the  molecules  of  mercury 
and  cadmium  contain  each  a  single  atom  only.  It  is  probable  that 
zinc  should  be  classed  with  mercury  and  cadmium. 

Vapor  Density.  Molec.  Wt.  Atomic  Wt.  ^Molecute8 
As                 150                  300                    75  4 

P  62       .  124  31  4 

Hg  100  200  200  1 

Cd  56  112  112  1 

If  this  view  of  the  molecular  structure  of  free  elementary  gases 
and  vapors  be  correct,  perfect  consistency  would  require  that  no 
equation  should  ever  be  written  in  such  a  manner  as  to  represent 
less  than  a  single  molecule  of  an  element  in  a  free  state  as 
either  entering  into  or  issuing  from  a  chemical  reaction.  Thus,  in- 
stead of  2  H  +  O  =  H20,  N  +  3  H  =N  H3,  HC1  +  Na  = 
NaCl  +  H,  it  would  be  necessary  to  write  2  H2  +  O2  =  2  H2O, 
N2  +  3  H2  =  2  NH3,  2  HC1  +  Na2  =  2  NaCl  +  H3. 

We  have  not  heretofore  conformed  to  this  theoretical  rule,  and  do 
not  propose  to  in  the  succeeding  pages,  and  this  for  two  reasons  :  first 
because  many  equations,  representing  chemical  reactions,  must  be 
multiplied  by  two,  in  order  to  bring  them  into  conformity  with  this 
hypothesis  concerning  molecular  structure  ;  the  equations  are  thus 
rendered  unduly  complex  ;  —  secondly,  because,  in  undertaking  to 
make  chemical  equations  express  the  molecular  constitution  of  ele- 
ments and  compounds,  as  well  as  the  equality  of  the  atomic  weights 
on  each  side  of  the  sign  of  equality,  there  is  imminent  danger  of  tak- 
ing the  student  away  from  the  sure  ground  of  fact  and  experimental 
demonstration,  into  an  uncertain  region  of  hypotheses  based  only  on 
definitions  and  analogies  ;  —  thirdly,  because  we  are  ignorant  of  even 


92  PHOSPHORUS.  [§141. 

the  probable  molecular  symbol  of  most  of  the  elements.  Of  all  the 
elementary  substances  recognized,  we  have  reason  to  believe  that 
eleven,  when  in  the  gaseous  state,  are  made  up  of  molecules  contain- 
ing each  two  atoms,  that  two  contain  four  atoms,  and  that  three  con- 
tain only  a  single  atom  to  the  molecule.  Of  the  molecular  structure 
of  the  remaining  elements,  numbering  three-fourths  of  the  whole,  we, 
at  present,  know  nothing. 

141.  Volumetric  interpretation  of  symbols. — This  important 
matter  forms  the  subject  of  §  517,  page  291,  but  it  should  be  studied 
as  apart  of  the  present  chapter,  as  should  also  §  518,  page  292. 


CHAPTER  XII. 
PHOSPHORUS  (P). 

142.  Phosphorus    occurs    somewhat    abundantly    and   very 
widely  diffused  in  nature.     It  is  never  found  in  the  free  state, 
but  almost  always  in  combination  with  oxygen  and  some  one 
of  the  metals.     The  most  abundant  of  its  compounds  is  calcium 
phosphate,  which  occurs  as  a  native  mineral  and  which  also 
forms  the  mass  of  the  mineral  constituents  of  the   bones  of 
animals.      The   small   amount    of    phosphorus   present   in   the 
soil  is  collected  by  the  growing  plants  ;  the  herbivorous  animals 
in  their  turn  consume  the  phosphorus  which  has  been  accumu- 
lated by  the  plants,  and  from  the  bones  of  animals  chemists 
and  manufacturers  derive  the  phosphorus  of  which  they  stand 
in  need. 

143.  Phosphorus,    when   perfectly   pure,    is   a   transparent, 
colorless,  wax-like  solid  of   1.8   specific  gravity,   which,   when 
freshly  cut,  emits  an  odor  like  garlic,  though  under  ordinary 
conditions   this    odor   is   overpowered   by  the    odor   of  ozone, 
which,   as   has    been   previously   stated    (§  103),    is    developed 
when  phosphorus  is  exposed  to  the  air.     It  unites  with  oxygen 


§  143.]  INFLAMMABILITY  OF  PHOSPHORUS.  93 

readily,  even  at  the  ordinary  temperature  of  the  air,  and  with 
great  energy  at  somewhat  higher  temperatures  (above  60°) ; 
when  in  contact  with  air,  it  is  all  the  while  undergoing  slow 
combustion. 

If  the  temperature  of  the  slowly -burning  phosphorus  be 
slightly  increased  in  any  way,  the  mass  will  burst  into  flame 
and  be  rapidly  consumed.  On  account  of  this  extreme  in- 
flammability, phosphorus  must  always  be  kept  under  water  : 
it  is  best  also  to  cut  it  under  water,  lest  it  become  heated  to 
the  kindling-point  by  the  warmth  of  the  hand,  or  by  friction 
against  the  knife  ;  for,  when  once  on  fire,  it  is  exceedingly 
difficult  to  extinguish  it,  and  in  case  it  happens  to  burn  upon 
the  flesh,  painful  wounds  are  inflicted,  which  are  very  difficult 
to  heal. 

On  account  of  this  easy  inflammability  by  friction,  phosphorus 
is  extensively  employed  for  making  matches.  The  matter  upon  the 
end  of  an  ordinary  friction-match  usually  contains  a  little  phosphorus, 
together  with  some  substance  capable  of  supplying  oxygen,  such  as 
red-lead,  black  oxide  of  manganese,  saltpetre  or  potassium  chlorate. 
The  phosphorus  and  the  oxidizing  agent  are  kneaded  into  a  paste 
made  of  glue  or  gum,  and  the  wooden  match-sticks,  the  ends  of  which 
have  previously  been  dipped  in  melted  sulphur,  are  touched  to  the 
surface  of  the  phosphorized  paste,  so  that  the  sulphured  points  shall 
receive  a  coating  of  it.  The  sulphur  serves  merely  as  a  kindling 
material,  which,  as  it  were,  passes  along  the  fire  from  the  phosphorus 
to  the  wood.  By  rubbing  the  dried,  coated  point  of  the  match  against 
a  rough  surface,  heat  enough  is  developed  to  bring  about  chemical 
action  between  the  phosphorus  and  the  oxygen  of  the  other  ingre- 
dient, combustion  ensues,  the  sulphur  becomes  hot  enough  to  take  on 
oxygen  from  the  air,  and  finally  the  wood  is  involved  in  the  play  of 
chemical  force. 

Exp.  57.  —  Put  a  piece  of  phosphorus  as  big  as  a  grain  of 
wheat  upon  a  piece  of  filter-paper,  and  sprinkle  over  it  some  lamp- 
black, or  powdered  bone-black.  The  phosphorus  will  melt  after  a 
time  and  will  finally  take  fire.  As  stated  above,  phosphorus  when 
exposed  to  the  air  is  all  the  time  undergoing  slow  combustion ;  this 
action  is  attended  by  evolution  of  heat.  Both  the  lampblack  and  the 
paper  are  bad  conductors  of  heat,  and  serve  to  prevent  the  phosphorus 


04  PHOSPHORESCENCE.  — RED  PHOSPHORUS.       [§  144. 

from  losing  that  developed  by  the  oxidation.  Moreover,  as  will  be 
explained  more  fully  hereafter  under  carbon,  the  vapor  of  phosphorus 
which  rises  continually  is  absorbed  by  or  dragged  into  the  pores  of  the 
bone-black  and  brought  into  intimate  contact  with  oxygen  which  is 
or  has  been  absorbed  from  the  air.  Chemical  action  ensues  between 
the  phosphorus  vapor  and  the  oxygen  gas,  and  as  the  heat  which  is 
generated  is  retained,  the  phosphorus  ultimately  takes  fire. 

144.  At  the  ordinary  temperature  of  the  air,  and  still  more 
at   somewhat   higher   temperatures,   phosphorus   shines  with   a 
greenish-white  light,  as  may  be  seen  by  placing  the  phosphorus 
in  the  dark;  hence  the  name,  phosphorus,  from  Greek  words 
signifying  light- bearing.     This  phosphorescence  is  seen  when  an 
ordinary  friction-match  is  rubbed  against  any  surface  in  a  dark 
room. 

145.  In  warm  weather  phosphorus  is  soft  and  somewhat  flexi- 
ble, and  may  then  be  bent  without  breaking.     It  melts  at  44°, 
forming  a  viscid  oily  liquid,  which  boils  at  .about  290°  and  is 
converted  into  colorless  vapor.     Phosphorus  can  readily  be  dis- 
tilled in  a  retort  filled  with  some  inert  gas,  like  hydrogen,  nitro- 
gen or  carbonic  acid.     When  heated  to  about  230°,  out  of  con- 
tact with  the  air,  phosphorus  is  converted  into  an  allotropic 
modification  known  as  red  phosphorus. 

Phosphorus  is  insoluble  in  water,  but  is  somewhat  soluble  in 
ether,  petroleum,  benzol,  oil  of  turpentine  and  other  oils  :  it  also 
dissolves  abundantly  in  carbon  bisulphide. 

If  a  solution  of  phosphorus  in  carbon  bisulphide  be  poured  upon  a 
sheet  of  filter-paper,  the  carbon  bisulphide  will  soon  evaporate,  leaving 
the  phosphorus  in  a  very  finely  divided  state.  The  phosphorus  begins 
immediately  to  oxidize,  and,  as  the  paper,  is  a  bad  conductor  of  heat, 
it  presently  will  burst  into  flame.  The  paper,  however,  is  not  com- 
pletely consumed,  but  a  very  considerable  residue  of  carbon  remains 
unburned.  This  depends  upon  the  fact  that  the  product  of  the  com- 
bustion of  the  phosphorus,  quickly  covers  the  paper  with  a  varnish 
which  is  not  only  incombustible  in  itself,  but  is  quite  impervious  to 
air. 

146.  Red  Phosphorus.  —  This   remarkable  allotropic  modifi- 
cation of  phosphorus  is  a  body  as  unlike  ordinary  phosphorus 


§  147.]  RED  PHOSPHORUS.  95 

in  most  respects  as  could  well  be  conceived.  It  is  of  a  scarlet- 
red  color,  has  neither  odor  nor  taste,  is  not  poisonous  so  far 
as  is  known,  is  not  phosphorescent,  does  not  take  fire  at 
ordinary  temperatures,  is  insoluble  in  bisulphide  of  carbon, 
and  in  general  behaves  altogether  differently  from  the  ordinary 
modification.  It  is  easy,  however,  to  convert  one  variety  into 
the  other.  If  ordinary  phosphorus  be  heated  to  230°  out 
of  contact  of  the  air,  the  red  variety  is  formed  :  if  this  be 
heated  still  further  to  260°,  it  changes  back  into  the  ordinary 
variety. 

Exp.  58.  —  In  a  narrow  glass  tube,  No.  6,  about  30  c.  m.  long 
and  closed  at  one  end,  place  a  quantity  of  red  phosphorus  as  large  as 
a  small  pea  ;  heat  the  phosphorus  gently  over  the  gas-lamp  and  note 
that  a  sublimate  of  a  light-colored  substance  is  quickly  deposited  upon 
the  cold  walls  of  the  tube  a  short  distance  above  the  heated  portion. 
This  light-colored  sublimate  is  ordinary  phosphorus,  as  may  be  shown 
by  cutting  off  the  tube  just  below  the  sublimate,  after  the  glass  has 
been  allowed  to  cool,  and  then  scratching  the  coating  with  a  piece 
of  wire  :  the  coating  will  take  fire.  The  air  in  the  narrow  tube  em- 
ployed is  deprived  of  its  oxygen  by  the  combustion  of  a  small  portion 
of  the  phosphorus  at  the  moment  of  its  transformation  from  the  red 
to  the  ordinary  condition  :  the  remaining  phosphorus  is  thus  enveloped 
in  nitrogen,  and  so  protected  from  further  loss. 

Red  phosphorus  is  employed,  to  a  certain  extent,  as  an  adjunct  to 
the  so-called  safety -matches.  Such  matches  contain  no  phosphorus  in 
themselves,  and  will  not  take  fire  readily  by  friction  upon  an  ordinary 
rough  surface,  though  they  burst  into  flame  at  once  when  rubbed  upon 
a  surface  specially  prepared  with  red  phosphorus.  The  matter  upon 
the  tips  of  safety-matches  is  usually  a  mixture  of  potassium  chlorate 
and  antimony  sulphide,  made  into  a  paste  by  means  of  glue  :  the  sur- 
face upon  which  the  match  is  to  be  rubbed  is  composed  of  red  phos- 
phorus, black  oxide  of  manganese  and  glue.  In  favor  of  the  use  of 
red  phosphorus  for  matches  are  the  facts,  that,  unlike  ordinary  phos- 
phorus, it  is  not  deleterious  to  the  workmen  who  have  to  deal  with  it, 
and  it  is  far  less  liable  to  be  set  on  fire  by  accidental  friction. 

147.  Phosphorus  combines  readily  with  many  other  elements 
besides  oxygen.  The  ordinary  modification  of  phosphorus  com- 
bines violently  with  sulphur  at  temperatures  near  the  melting- 


96  HYDROGEN  PHOSPHIDE.  [§  14& 

point  of  sulphur,  the  act  of  combination  being  attended  with 
vivid  combustion  and  loud  explosion.  With  chlorine,  bromine 
and  iodine,  ordinary  phosphorus  unites  directly  at  the  ordinary 
temperature  of  the  air?  the  combination  being  rapid  and  attended 
with  inflammation.  Phosphorus  unites  directly  with  most  of 
the  metals  forming  phosphides. 

148.  Compounds  of  Phosphorus  and  Hydrogen.  —  There  are 
three  compounds,  of  phosphorus  and  hydrogen  ;  of  which-  at 
ordinary  temperatures,  one  is  gaseous,  H3P,  one  liquid,  H2P, 
and  one  solid,  HP2.  The  gaseous  compound,  or  rather  the 
gaseous  compound  charged  with  the  vapor  of  the  liquid  com- 
pound, is  somewhat  interesting,  from  the  fact  that  it  takes 
fire  spontaneously,  immediately  on  coming  into  contact  with 
the  air. 

Exp.  59.  —  In  a  thin-bottomed  flask  of  about  140  c.  c.  capacity 
put  1  grm.  of  phosphorus  and  115  c.  c.  of  hydrate  of  sodium, 
obtained  by  dissolving  40  grins,  of  common  caustic  soda  in  110 
c.  c.  of  water.  Pour  two  or  three  drops  of  ether  upon  the  liquid  in 
the  neck  of  the  flask,  then  close  the  flask  with  a  cork  carrying  a  long 
delivery-tube  of  glass,  No.  5.  Place  the  flask  over  the  gas-lamp,  upon 
the  wire-gauze  ring  of  the  iron  stand,  and  immerse  the  end  of  the 
delivery-tube  in  the  water-pan,  then  gently  heat  the  flask.  The  ether 
is  added  to  the  contents  of  the  flask,  in  order  that  the  last  traces  of 
air  may  be  expelled  from  the  flask  by  the  vapor  which  arises  from 
this  highly  volatile  liquid  as  soon  as  it  is  warmed. 

Fig.  30.  As  the  potash-lye  be- 

comes hot,  small  bub- 
bles of  gas  will  be  seen 
to  arise  from  the  sur- 
face of  the  phosphorus, 
and  in  a  short  time 
large  bubbles  of  gas  will 
escape  from  the  deliv- 
ery-tube :  each  of  these 
bubbles,  as  it  comes  in 
contact  with  the  air  at 
the  surface  of  the  water, 
will  spontaneously  burst  into  flame,  and  burn  with  a  vivid  light  and 


§  149.]  OXIDES  OF  PHOSPHORUS.  97 

the  formation  of.  beautiful  rings  of  white  smoke,  if  the  air  be  not  dis- 
turbed by  draughts.  In  burning,  the  hydrogen  phosphide  is  con- 
verted into  phosphoric  acid,  and  of  this  product  the  white  smoke 
is,  of  course,  composed. 

2  H3F  +80  =  2  H3F04. 

The  atomic  weight  of  phosphorus  is  31  ;  the  specific  gravity  of  its 
vapor  has  been  found  to  be  62.1.  In  this  respect  phosphorus  differs 
from  the  elements  already  studied  where  the  combining  weights  and 
the  unit-volume  weights  have  been  identical  ;  it  follows  that,  if  the 
molecule  of  hydrogen  contains  two  atoms  of  hydrogen,  the  molecule 
of  phosphorus  will  contain  four  atoms  of  phosphorus  (p.  91).  If  we 
compare  the  formula  of  hydrogen  phosphide,  H3P  (§  148),  with  that 
of  ammonia,  H3N,  we  have  the  atom  of  phosphorus,  which  weighs  31, 
combining  with  the  same  quantity  of  hydrogen  by  weight  as  the  atom 
of  nitrogen  ;  but  while  from  two  volumes  of  ammonia-gas  we  may 
set  free  three  volumes  of  hydrogen  and  one  volume  of  nitrogen,  from 

two  volumes  of  hydrogen 
phosphide  we  have  three  vol- 
umes of  hydrogen  and  only 
half  a  volume  of  phosphorus 
vapor.  The  composition  of 
hydrogen  phosphide  may 
thus  be  represented  by  the 
accompanying  diagram. 


H 

1 


149,  Oxides  of  Phosphorus. — There  are  three  oxides  of 
phosphorus  answering  to  the  fornmlge  P2O,  P2O3,  P2O6. 

Hypophosphorous  Anhydride  (P2O).  —  It  is  doubtful  whether 
this  oxide  has  been  isolated.  The  corresponding  acid,  however, 
H3FO2  (3  H2O,  P2O  —  2  H3PO2),  is  known,  as  are  also  the  corre- 
sponding salts,  the  hypophosphites  of  certain  metals  :  the  hypo- 
phosphite  of  barium,  for  instance,  is  Ba  H4P2O4. 

Phosphorous  Anhydride  (P2O3)  is  formed  by  burning  phos- 
phorus with  a  limited  supply  of  air.  It  is  a  white  amorphous  sub- 
stance, very  soluble  in  water,  and  burning  in  the  air  to  phosphoric 
anhydride  (P2O5).  The  corresponding  acid  is  H3PO3  (3  H2O,  P2O3) 
and  the  corresponding  salts  are  called  phosphites. 
9 


98  OXIDES  OF  PHOSPHORUS.  [§  150. 

150.  Phosphoric  Anhydride  (PaO6). — This,  oxide  of  phos- 
phorus is  the  product  of  the  rapid  combustion  of  phosphorus  in 
an  excess  of  air  or  oxygen. 

Exp.  60.  —  Dry  thoroughly  a  large  porcelain  plate,  a  small  porce- 
lain capsule  and  a  wide-mouthed  bottle  of  two  litres'  capacity,  by 
Fig.  31.  warming  them  at  a  fire  ;  place  the  capsule  upon 

the  plate  and  put  in  the  capsule  a  bit  of  dry 
phosphorus,  of  the  weight  of  about  half  a 
gramme  ;  light  the  phosphorus  and  cover  it  at 
once  with  the  inverted  bottle.  The  phosphoric 
anhydride,  formed  by  the  combustion  of  the 
phosphorus,  will  be  deposited  as  a  white  pow- 
der, like  flakes  of  snow,  upon  the  sides  of  the 
bottle,  and  much  of  it  will  fall  down  upon  the 
plate  below. 

The  flocculent,  amorphous,  odorless  powder,  thus  obtained, 
unites  with  water  with  remarkable  facility  :  if  it  be  left  in  the 
air  for  a  few  minutes,  it  deliquesces  completely  ;  upon  being 
thrown  into  water,  it  dissolves  with  a  hissing  noise  and  de- 
velopment of  much  heat.  In  order  to  preserve  it,  it  must  be 
placed  in  a  dry  tube,  and  the  tube  closed  by  sealing  it  in  the 
lamp. 

151.  Phosphoric  Acid.  —  By  the  union  of  phosphoric  anhy- 
dride with  water,  there  are  formed  three  distinct  acids  :  meta- 
phosphoric  acid   (HPO8),   pyro-phosphoric   acid   (H4P2O7)   and 
ordinary  or  tribasic  phosphoric  acid  (H3PO4).     Corresponding 
to  these  three  varieties  of  phosphoric  acid,  there  are  three  series 
of  phosphates,  the  meta-phosphates,  the  pyro-phosphates  and  the 
ordinary  phosphates. 

The  number  of  possible  phosphates  is  much  increased  from  the 
fact  that  while  meta-phosphoric  acid  (HPO3),  like  nitric  acid,  is 
monobasic,  pyro-phosphoric  acid  (H4P2OT)  is  tetrabasic,  i.e.,  has 
four  replaceable  atoms  of  hydrogen,  and  the  ordinary  phosphoric  acid 
(H3P04)  is  tribasic.  (See  §  134.) 

152.  Empirical  and  Rational  Formulae.  —  It  has  already  been 
stated   that   when   phosphoric  anhydride   is  thrown   into   water,  it 
unites  with  a  portion  of  the  water  to  form  phosphoric  acid.     The 


§  152.]       EMPIRICAL  AND  RATIONAL  FORMULA.  99 

reaction  may  be  thus  symbolized  :  F2O5  -|-  H2O  =  H2O,  P2O5  = 
H2P2O6  =  2  HPO3  (meta-phosphoric  acid).  .  If  the  anhydride  be 
thrown  into  hot  water,  the  reaction  is  P2O5  -\-  3  H2O  =  3  H2O,  P2O5 
=  H6P2O8  =  2  H3PO4  (ordinary  phosphoric  acid).  We  may  rep- 
resent meta-phosphoric  acid  by  the  formula  H2O,  P2O6  or  by  HPO3 ; 
we  may  represent  ordinary  phosphoric  acid  by  3  H0O,  P2O5  or  by 
H3FO4  :  in  these  cases  we  have  two  formulae  to  denote  one  and  the 
same  substance.  If  ordinary  phosphoric  acid  were  analyzed,  it  would 
be  found  to  contain,  for  every  three  parts  by  weight  of  hydrogen, 
-thirty-one  parts  of  phosphorus  and  sixty-four  (4  X  16)  parts  of  oxy- 
gen. The  result  of  the  analysis  would  be  expressed  most  simply  by 
the  formula  H3PO4. 

A  formula  which  simply  represents  the  number  of  atoms  of  each 
element  in  one  molecule  of  any  substance,  as  determined  by  analysis, 
is  called  an  empirical  formula.  The  truth  of  such  a  formula  de- 
pends solely  upon  the  correct  performance  of  the  analytical  process, 
and  upon  the  accuracy  with  which  the  atomic  weights  have  been 
determined.  Concerning  such  formulae,  there  is  little  room  for  dif- 
ference of  opinion  :  they  express  all  that  we  actually  know  of  the 
elementary  composition  of  any  compound  body.  Chemists  have, 
however,  endeavored  to  contrive  formulae  which  should  express 
something  more  than  the  mere  elementary  composition  by  weight  ; 
which  should  recall  the  materials  from  which  the  formulated  sub- 
stance was  made,  and  prophesy  the  products  of  its  decomposition  ; 
which  should  not  only  name  and  number  the  atoms  of  the  sub- 
stance, but  should  also  suggest  such  a  grouping  or  arrangement  of 
those  atoms  as  might  serve  to  interpret  its  known  reactions.  Such 
formulae  are  called  rational  formulae.  In  the  present  case  3  H2O, 
P2O5  is  a  rational  formula  of  phosphoric  acid.  It  recalls  the  fact 
that  the  acid  can  be  made  by  causing  phosphoric-  anhydride  to  unite 
with  water. 

It  is  not  altogether  a  matter  of  indifference  whether  phosphoric 
acid  be  written  3  H2O,  P2O5  or  H3PO4  ;  for  in  one  case  the  weight 
of  the  molecule  would  be  196  and  in  the  other  98.  If  it  were  possible 
to  obtain  this  compound  in  the  state  of  vapor,  and  the  vapor  could  be 
weighed,  the  weight  of  the  molecule  could  be  found  (§  139)  by  multi- 
plying the  vapor  density  by  two.  It  is  usual  to  regard  the  shorter 
formula  as  representing  the  molecule.  The  same  difficulty  occurs  in 
the  case  of  other  compounds,  nitric  acid,  for  instance  •  the  molecule 
of  nitric  acid  may  be  H2O,  N2O5  =126  or  HNOa  =  63.  In  some 


100  DUALISTIC  AND   TYPICAL  FORMULA.          [§  153. 

reactions  it  is  more  convenient  to  employ  one  formula,  and  in  other 
reactions  the  other  formula. 

It  is  evident  that  there  may  be  various  rational  formulae  for 
the  same  substance  :  in  fact,  for  acetic  acid,  a  compound  of  carbon, 
oxygen  and  hydrogen  to  be  described  in  a  subsequent  chapter,  no 
fewer  than  nineteen  formulae  have  been  proposed. 

153.  All  the  acids  (except  those  formed  by  the  union  of  hydrogen 
with  members  of  the  chlorine  group)  and  the  corresponding  salts  may 
be  written  in  a  manner  similar  to  that  employed  in  the  case  of  phos- 
phoric  acid  3  H2O,  P2O5 :  thus,  —  nitric  acid,  H,O,  N2O5  ;   sodium 
nitrate,   Na2O,  N2O5  ;    potassium    sulphate,    K.,O,  SO3.      Such    for- 
mulae are  called  dualistic,   because  they  represent  these  bodies  as 
of  a  dual  nature,  —  as  being  made  up  of  two  oxides  which  were  dis- 
tinct before  they  wrere  brought  together  to  form  the  compound,  and 
will  be  distinct  when  separately  extracted  from  it  :  in  a  dualistic  for- 
mula these  two  distinct  parts  are  conventionally  represented  as  having 
some  separate  existence  within  the  compound  itself.     The  supposition 
is  not  unnatural  :  thus,  for  example,  common  plaster  of  Paris  is  a  sub- 
stance containing  the  metal  calcium  and  the  elements  sulphur  and 
oxygen  in  the  proportions  by  weight  which  are  correctly  expressed  by 
the  formula  CaSO4 ;  but  this  substance  may  be  made  by  methods 
which  suggest  another  formula.     If  we  put  together  quicklime,  CaO, 
and  sulphuric  anhydride,  SO3,  in  due  proportions,  under  suitable 
conditions,  plaster  of  Paris,  or,  as  its  chemical  name  is,  calcium  sul- 
phate,  results  :    CaO  -j-  SO8  =  CaO,   SO3 ;    or  if  we  mix   slaked 
lime,  CaO,  H2O,  with  sulphuric  acid,  H2O,  SO3,  in  proper  propor- 
tions, at  a  suitable  temperature,  we  shall  again  obtain  calcium  sul- 
phate, and   water   will   be    eliminated  :    CaO,  H0O  -f-  H2O,  SO8  = 
CaO,  S03  -f-  2  H20. 

154.  Another  way  of  writing  chemical  formulae  is  in  accordance 
with  the  doctrine  of  types.     According  to  this  doctrine,  every  pos- 
sible chemical  combination  may  be  imagined  to  be  built  upon  the 
plan,  or  framed  upon  the  type  or  model,  of  some  one  of  three  sub 
stances,  chlorhydric  acid  (or  free   hydrogen),  water  and   ammonia. 
These  substances  must  be  regarded  as  types  only  with  reference  to 
the  supposed  grouping  of  atoms  in  the  compounds  :   the  external 
properties  of  various  substances  referred  to  the  same  type  may  be 
totally  different.     Examples  of  compounds  referred  to  the  different 
types  are  :  — 


§154.]  TYPICAL  FORMULA.  —  HA'DICALS.    •  V'    J    it'l 

Type.  Free  Sodium     '  Methyl 

Chlorhydric  acid.  Hydrogen.  chloride.  hydride. 

H  )  H    )  Na  )  (CH3)  ) 

ci]  H  |  ci  j  H  } 

Type.  Sodium  Nitric 

Water.  hydrate.  acid.  Alcohol. 

H|o  » 

Type. 

Ammonia.                     Aniline.  Methylamine.  Acetamide. 

(C6H5))  (CH3))  (C2H30)) 

H     }N  H     \N  H  IN 

H     )  H    )  H  ) 

It  will  be  noticed  in  these  examples  that  the  hydrogen  of  the  type 
may  be  replaced,  not  only  by  a  single  element,  but  also  by  a  group  of 
elements.  Such  groups  of  elementary  atoms  are  called  compound 
radicals,  and,  like  the  elementary  atoms  themselves,  differ  in  their 
replacing  power,  some  being  uniwdent,  some  bivalent,  etc. 

The  typical  formula  of  some  substances  is  written  by  regard- 
ing the  substance  as  built  upon  the  type  of  the  double  molecule  of 
the  typical  compound  :  other  substances  are  regarded  as  built  upon  a 
mixed  type.  The  following  examples  will  serve  to  illustrate  a  few  of 
these  cases  :  — 

Type.  Sulphuric  Calcium  Lead 

acid.  sulphate.  nitrate. 


Type. 

Urea. 

%1N 

H;$ 

<c|r; 

N2 

Type. 

Sulphurous 

acid. 

H  ( 

H 

) 

H  \ 

(SO,)  " 

fb 

Type.  Glycerin. 

HJ0  (C3H5)"' 

H3J°«  H8 


It  is  often  convenient  to  mark  the  fact  that  an  elementary  atom 
or  a  radical  is  bivalent  or  trivalent  by  the  use  of  the  proper  number 
of  accents  placed  at  the  right  hand  of  the  symbol,  as  has  been  done 
in  these  examples. 

These  typical  formulae  will  be  found  especially  useful  in  the  consid- 
9* 


AHSENIDE. 


[§  155. 


eration  of  the  compounds  of  carbon  ;  it  is,  however,  to  be  distinctly 
remembered  that  a  rational  formula  is  never  to  be  regarded  as  the 
expression  of  an  absolute  truth,  but  only  as  a  guide  in  classification, 
an  aid  to  the  memory  and  a  help  in  instruction  ;  while  the  empirical 
formula  expresses  all  that  is  actually  known  of  the  composition  of 
any  given  body. 


CHAPTER   XIII. 
ABSENIC,  ANTIMONY  AND  BISMUTH. 

ARSENIC    (AS). 

155.  In  small  quantity  arsenic  is  very  widely  distributed  in 
nature.     It  is  sometimes  found  free  in  the  metallic  state,  but 
generally  in  combination  with  oxygen  or  sulphur  and  some  one 
of  the  metals,  such  as  iron,  cobalt,  nickel  and  copper. 

156.  Arsenic    is    a   brittle  solid   of   a   steel-gray  color  and 
metallic  lustre.     At  a  dull  red  heat  it  may  be  converted  into  a 
vapor  which  has  a  peculiar  garlic  odor.     Heated  in  the  air  or 
in  oxygen,  arsenic  burns  with  a  whitish  flame  producing  the 
white  arsenic  teroxide  (arsenious  anhydride).     Arsenic  com- 
bines readily  with  chlorine,  bromine,  iodine  and   sulphur;    it 
also  unites  by  fusion  with  most  metals,  forming  alloys,  which 
the  arsenic  tends  to  make  hard  or  brittle.     In  the  manufacture 
of  shot,  a  little  arsenic  is  added  to  the  lead  to  facilitate  the  for- 
mation of  regular  globules. 

The  symbol  of  arsenic  is  As ;  its  atomic  weight  is  75.  Like 
phosphorus,  the  specific  gravity  of  its  vapor  is  double  its  atomic 
weight,  and  consequently  its  molecular  symbol  is  As4. 

157.  Hydrogen  arsenide  or  arseniuretted  hydrogen  (H3As) 
is  a  colorless  gas,  having  a  fetid  odor  :  even  when  very  much 
diluted  with   air,    it  is   intensely  poisonous,    and  fatal  results 
have  repeatedly  followed  its   accidental   inhalation.      The  gas 
may  be  prepared  in  an  impure  state  mixed  with  hydrogen  by 
introducing   a  solution  of    some   compound  of   arsenic   into  a 


§  159.]    HYDROGEN  ARSENIDE.  -  OXIDES  OF  ARSENIC.     103 

generator  in  which  hydrogen  is  being  produced  from  zinc  and  a 
dilute  acid. 

Hydrogen  arsenide  burns  in  the  air  with  a  whitish  flame, 
forming  water  and  a  white  smoke  of  arsenious  anhydride  ; 
but  if  a  cold  body,  like  a  piece  of  porcelain,  for  example,  be 
introduced  into  a  jet  of  the  burning  gas,  the  hydrogen  alone 
will  burn,  and  the  arsenic  will  be  deposited  in  the  metallic 
state  upon  the  porcelain  surface,  forming  a  lustrous  black  spot. 
This  effect  is  precisely  similar  to  the  deposition  of  soot  on  a 
cold  body  held  in  the  flame  Fig'  38* 

of  a  candle.  The  gas  is  also 
decomposed  when  caused  to 
pass  through  tubes  heated 
to  dull  redness,  metallic 
arsenic  being  deposited  as 
a  brown  or  blackish  mirror, 
while  hydrogen  gas  escapes. 
These  properties  of  hydro- 
gen arsenide  are  made  use  of  in  testing  for  the  presence  of 
arsenic  in  cases  of  suspected  poisoning. 

158.  Compounds  of  Arsenic  and  Oxygen.  —  There  are  two 
well-defined  oxides  of  arsenic,  —  arsenious  anhydride  (As2O3) 
and  arsenic  anhydride  (As2o5). 

159.  Arsenious   anhydride   (AsaO3)   often   called   arsenious 
acid,  or  white  arsenic,  is  formed  when  metallic  arsenic  or  arseni- 
cal ores  are  heated  in  the  air.     It  ordinarily  occurs  in  small 
octahedral  crystals.     When  heated  with  free  access  of   air,  it 
volatilizes  without  change  :  if  heated  in  contact  with  carbon,  it 
gives  up  its  oxygen,  and  metallic  arsenic  is  liberated.     Arsenious 
anhydride  is  somewhat  soluble  in  water :  it  dissolves  readily  in 
hot  chlorhydric  acid  ;  but,  when  the  solution  cools,  most  of  the 
arsenious  anhydride  is  deposited  unchanged. 

Exp.  61.  —  Place  a  few  particles  of  "  arsenious  acid  "  *  in  an  open 

*  The  substances  now  designated  as  anhydrides  were  formerly  called  acids 
as  stated  in  §  63.  In  the  case  of  sulphurous,  arsenious  and  carbonic  anhydrides, 
the  popular  names  sulphurous,  arsenious  and  carbonic  acids  have  such  currency 
that  they  will  be  employed  in  this  Manual  where  no  ambiguity  can  arise  froni 
such  use. 


104  ARSENIOUS  ACID.— ARSENITES.  [§160. 

tube  of  hard  glass  (No.  5)  about  10  c.  m.  long,  and  heat  over  the 
lamp,  holding  the  tube  in  a  sloping  position  :  the  white  solid  will  be 
volatilized,  but  it  will  immediately  be  deposited  again  upon  the  cold 
part  of  the  tube.  By  the  aid  of  a  lens,  this  deposit  may  be  seen  to 
be  crystalline. 

Fis.  33.  Exp.   62.  —  Drop   into    the    point 

of  a  drawn-out  tube  of  hard  glass, 
No.  5,  a  morsel  of  arsenious  acid,  and 
above  it  place  a  splinter  of  charcoal 
(Fig.  33)  ;  heat  the  coal  red-hot  in 
the  flame  of  the  lamp,  and  then  vola- 
tilize the  arsenious  acid.  The  acid 
will  give  its  oxygen  to  the  coal,  and 
the  arsenic  will  be  deposited  in  a  ring 
on  the  cold  part  of  the  tube,  presenting  a  brilliant  metallic  appear- 
ance. 

Exp.  63.  —  Throw  a  particle  of  arsenious  acid  upon  a  piece  of 
red-hot  charcoal  :  the  acid  will  be  partly  reduced,  and  the  peculiar 
garlic  odor  of  the  vapor  of  metallic  arsenic  will  be  perceived. 

160.  Arsenious  acid  is  a  violent  poison,  all  the  more  dan- 
gerous, because  it  has  neither  taste  nor  odor  to  warn  the  victim 
of  its  presence  :  two  decigrammes  of  it  will  cause  death.     All 
the  soluble  salts  of  arsenious  acid  are  likewise  horribly  poison- 
ous.    The  best  antidote  to  the  poison  is  a  mixture  of  moist, 
freshly  precipitated  iron  hydrate  and  caustic  magnesia. 

Arsenious  acid  is  largely  used  in  the  manufacture  of  a  bril- 
liant green  pigment,  a  compound  of  arsenite  and  acetate  of  copper, 
commonly  called  Paris  green ;  it  is  applied  as  an  oxidizing  agent 
in  the  manufacture  of  glass  ;  it  is  consumed  in  considerable  quan- 
tities for  poisoning  vermin,  and  for  producing  the  arsenic  acid 
which  is  used  in  the  dyeing  and  printing  of  cloth ;  it  is 
used  in  very  small  doses  as  a  remedy  for  asthma,  and  in  some 
skin  diseases. 

161.  Arsenious  anhydride  is  soluble  in  water.     The  solution 
is  slightly  acid,  but  it  is  doubtful  whether  a  definite  compound  of  the 
anhydride  with  the  elements  of  water  is  formed  ;  if  so,  it  would  be 
properly  designated  as  arsenious   acid  :  there  are  compounds  of 
various  metals  (called  arsenites)  which  would  imply  an  arsenious 
acid  of  the  formula  H3AsO3.     Thus  silver  arsenite  is  Ag3AsOg. 


§  165.]  ANTIMONY.  105 

1.62.  Arsenic  anhydride  (As2O5)  is  prepared  by  heating  arse- 
nic acid  to  dull  redness.  It  forms  a  white  amorphous  mass,  which 
by  long  exposure  to  water  is  gradually  converted  back  into  arsenic 
acid. 

Arsenic  acid  (H3AsO4)  is  obtained  by  oxidizing  arsenic-us 
anhydride  with  nitric  acid,  aqua  regia  or  other  oxidizing  agents. 
The  corresponding  suits  of  the  metals  are  called  arseniates.  Arsenic 
acid  and  some  of  the  arseniates  are  used  in  dyeing. 

163.  Sulphides  of  Arsenic.  —  Two  sulphides  of  arsenic  occur 
native,  one  (As2S2)  is  called  realgar.     It  is  used   in   pyrotechny. 
The  other  (As2S3)  is  called  orpiment.     It  is  also  prepared  artifi- 
cially, and  is  used  somewhat  as  a  pigment. 

ANTIMONY    (gb). 

164.  Antimony,  like  arsenic,  is  found  native  :  it  also  occurs 
alloyed  with  other  metals,  especially  with  arsenic,  nickel  and 
silver.      There   exist  also   a  considerable  number  of  minerals, 
which  consist  of,  or  contain,  large  proportions  of  the  compounds 
of  antimony  with  oxygen  and  sulphur.     All  the  antimony  of 
commerce  is  obtained  from  the  mineral  tersulphide,  Sb2S3.     The 
symbol  for  antimony  is  Sb,  from  the  Latin  name  of  the  sub- 
stance, Stibium. 

165.  Antimony   is   a   brittle    metal,   having   a   bluish-white 
color,  a  brilliant  lustre  and  a  highly  crystalline  structure.     The 
cakes  of  the  commercial  metal  usually  present  upon  their  upper 
surfaces   beautiful    stellate   or    fern-like  markings.      Antimony 
melts  at  450°,   gives  off  vapors  at  a  low  red  heat  and  takes 
fire  at  full  redness,  burning  brilliantly  with  -evolution  of  white 
fumes  of  the  teroxide  (Sb2O3).     The  atomic  weight  of  antimony 
is  120. 

Antimony  enters  into  the  composition  of  several  very  valu- 
able alloys.  Type  metal  is  an  alloy  of  lead  and  antimony, 
containing  about  20  per  cent  of  antimony.  For  stereotype 
plates  -fa  to  -fa  of  tin  is  usually  added  to  this  alloy.  The  com- 
mon white  metallic  alloys,  such  as  Britannia  metal,  pewter, 
etc.,  used  for  cheap  teapots,  spoons,  forks  and  like  utensils, 
are  variously  compounded  of  brass,  tin,  lead,  bismuth  and  an- 


106  COMPOUNDS  OF  ANTIMONY.  [§  166. 

timony.  The  value  of  antimony  in  these  alloys  depends  upon 
the  hardness  which  it  communicates  to  the  compounds,  without 
rendering  them  inconveniently  brittle. 

166.  Hydrogen  antimonide  (H3Sb  ?)  is  a  colorless,  inodorous 
gas  which  resembles  hydrogen  arsenide  in  being  decomposed  by 
heat  ;  it  bums  in  the  air  with  a  whitish  flame  and  gives  off  a  smoke 
of  antimony  teroxide  :  when  a  bit  of  cold  porcelain  is  held  against 
a  burning  jet  of  the  gas,  a  sooty  spot  of  metallic  antimony  is  deposited 
on  the  porcelain.     These  spots  of  metallic  antimony  are  distinguished 
from  those  of  arsenic,  obtained  in  a  similar  manner  from  hydrogen 
arsenide  by  difference  in  lustre,  volatility  and  solubility  in  various 
chemical  agents. 

167.  Antimony   and   Oxygen.  —  Antimony    forms    two    well- 
defined    oxides,  —  antimony   teroxide    (Sb2O3)    and    antimonic 
anhydride  (Sb2O5).     Antimony  teroxide  occurs  as  a  native  min- 
eral, and  is  formed  when  metallic  antimony  is  burned  in  the  air. 
Antimonic   anhydride   is   formed  by   heating  antimonic   acid. 
The  acid  may  be  obtained  by  oxidizing  metallic  antimony  with  nitric 
acid.     A   third   oxide   of  antimony   occurs  native.     Its  formula  is 
Sb2O4  and  it  may  be  regarded  as  a  compound  of   the  other  two 
oxides,  —  Sb2O3,  Sb2O5  =  2  Sb2O4. 

168.  Antimony  and  Chlorine. — Powdered  antimony  takes 
fire  when  thrown  into   chlorine   gas   (Exp.  32,  §  81) ;    it  also 
combines  very  energetically  with  bromine  and  iodine.    When  very 
finely  powdered,  it  is  dissolved  by  boiling  chlorhydric  acid,  with 
evolution  of  hydrogen  ;  if  a  little  nitric  acid  be  added  to  the 
chlorhydric,  the  metal  dissolves   easily,  to  form  a  solution  of 
antimony  terchloride  (SbCl3). 

Antimony  terchloride  at  the  ordinary  temperature  is  a  trans- 
Fig.  34.  lucent  yellowish  substance  of  fatty  consistency, 
whence  its  popular  name,  "  butter  of  antimony." 
When  thrown  into  water,  it  is  decomposed  into 
chlorhydric  acid  and  antimony  teroxide,  which, 
however,  remains  united  with  a  portion  of  the 
chloride,  forming  a  white  powder  which  contains 
antimony,  chlorine  and  oxygen,  but  is  somewhat 
variable  in  composition.  *" 

Exp.  64.  —  In   a  flask  of  about  200  c.  c.  ca- 
pacity, heat  gently  0.5  grin,  of  finely-powdered 


§  172.]  BISMUTH.  107 

antimony  with  30  c.  c.  of  strong  chlorhydric  acid,  to  which  10  drops 
of  nitric  acid  have  been  added.  When  complete  solution  has  been 
effected,  pour  a  little  of  the  chloride  into  water,  to  demonstrate  the 
decomposition  just  referred  to.  Evaporate  the  rest  of  the  solution  to 
the  consistency  of  a  thick  sirup  :  it  is  the  butter  of  antimony. 

169.  Antimony  and  Sulphur.  —  The  native  mineral  known  as 
gray  antimony  or  antimony  glance  is  antimony  tersulphide 
(Sb2S3).     It  is  the  source  of  the  antimony  of  commerce. 

BISMUTH    (fii). 

1 70.  The  metal  bismuth  is  found  chiefly  in  the  metallic  state, 
but  also  occurs  in  combination  with  sulphur,  oxygen  and  tel- 
lurium.    It  is  prepared  for  the  arts  almost   exclusively  from 
native   bismuth.     It  is  a  tolerably  hard,  brittle  metal,  of  a 
grayish-white  color  with  a  reddish  tinge.     When  pure,  it  crys- 
tallizes more  readily  than  any  other  metal ;  by  the  method  of 
fusion  (§  113)  it  may  be    obtained  in  most  beautiful  crystals, 
made  highly  iridescent  by  the  thin  film  of  oxide  which  forms 
on  their  surfaces  while  they  are  still  hot. 

Bismuth  promotes  the  fusibility  of  metals  with  which  it  is 
alloyed  to  an  extraordinary  extent.  The  most  remarkable  alloy 
of  bismuth  is  that  known  as  "  fusible  metal."  When  composed 
of  1  part  of  lead,  1  part  of  tin  and  2  parts  of  bismuth,  this 
alloy  melts  at  93°. 75.  The  symbol  of  bismuth  is  Bi  ;  its  atomic 
weight  is  210. 

171.  There  is  no  compound  of  bismuth  and  hydrogen  as  yet  known. 
There  are  three  oxides  corresponding  to  the  oxides  of  antimony,  —  bis- 
muth teroxide  (Bi2O3),  bismuthic  anhydride  (Bi2O5)  and  the  oxide 
Bi2O4  which  may  be  regarded  as  a  compound  of  the  other  two.     Bis- 
muth terchloride  (BiCl3)  resembles  antimony  terchloride.     It  is  de- 
composed by  water  into  chlorhydric  acid,  which  dissolves  a  portion 
of  the  chloride,  and  a  precipitate  containing  bismuth,  chlorine  and 
oxygen,  and  called  bismuth  oxy chloride  (BiOCl). 

172.  The  Nitrogen  Group  of  Elements.  —  The  five  elements, 
nitrogen,  phosphorus,  arsenic,   antimony  and  bismuth,  form  a 
well-marked  natural  group  of  elements.     In  the  first  place,  the 
elements  themselves  exhibit  a  definite  gradation  of  properties., 


108  THE  NITROGEN  GROUP.  [§  172. 

and,  secondly,  the  analogy  in  composition  and  properties  mani- 
fested by  the  similar  compounds  of  the  five  elements  is  most 
striking  and  complete. 

Nitrogen  is  a  gas,  phosphorus  a  solid  whose  specific  gravity 
varies  from  1.8  to  2.2,  arsenic  has  the  specific  gravity  of  5.6, 
antimony  of  6.7,  while  that  of  bismuth  rises  to  9.8.  The  me- 
tallic character  is  most  decided  in  bismuth,  is  somewhat  less 
marked  in  antimony,  is  doubtful  in  arsenic  and  almost  van- 
ishes in  phosphorus.  The  series  of  corresponding  hydrides, 
oxides,  chlorides  and  sulphides,  which  the  elements  of  this 
group  form,  are  very  perfect  :  they  prove  the  general  chemical 
likeness  of  the  five  elements  :  — 

Hydrides.         Oxides.          Oxides.          Oxides.         Chlorides.  Sulphides. 

NHd  N203  N204  N205  NC13(0  P2S3 

PH3  F203  Sb204          P205  PC13  As2S8 

AsH3          As203          Bi204  As2O5          AsCl3  Sb2S3 

SbH3          Sb203  Sb205          SbCl3  Bi,S3 

BiCl3 


PC15  As2S5 

SbCl5  Sb2S5 

When  the  qualities  of  the  corresponding  compounds  which 
the  members  of  the  nitrogen  group  form  with  other  elements 
are  duly  taken  into  account,  it  will  be  apparent  that  the  relative 
chemical  power  of  each  element  of  the  group  may  be  inferred 
from  its  position  in  the  series  of  elements  :  — 

N  =  14,  P  =  31,  As  =  75,  Sb  =  122,  Bi  =  210. 

The  chemical  energy  of  these  five  elements,  broadly  considered, 
follows  the  opposite  order  of  their  atomic  weights. 


§  175.]  CARBON.  109 

CHAPTER   XIV. 
CAEBON  (C). 

173.  Carbon  is  an  extremely  important  and  a  very  abundant 
element.     All  organic  substances,  all   things  which  have  life, 
contain  it.     In  the  mineral  kingdom,  the  various  forms  of  coal, 
graphite,  petroleum,  asphaltum,  and  all  the  different  varieties  of 
limestone,  chalk  and  marble,  contain  it  in  large  proportion.     It 
is  found  also  in  the  atmosphere  and  in  the  waters  of  the  globe, 
and  though  existing  therein  in  comparatively  small  proportion, 
it  is  an  ingredient  not  less  essential  than  either  of  their  other 
constituents  for  the  maintenance  of  the  actual  balance  of  organic 
nature.     All  vegetable  life  is  directly  dependent  upon  the  pres- 
ence of  the  compound  of  carbon  (carbonic  acid)  which  exists 
in  the  atmosphere. 

174.  Three    distinct    allotropic    modifications    of    carbon 
are   distinguished,    namely,    1.    The   diamond;    2.    Plumbago 
or  graphite ;  and  3.    Ordinary  charcoal  or  lamp-black ;    of 
this  last  modification  there  are   many  sub- varieties.     In  each 
of  its  modifications,  carbon  is  an  infusible,   non-volatile  solid 
devoid   of  taste   and   smell.     While   the  several  modifications 
differ  among  themselves  in  color,  hardness,  lustre,  specific  grav- 
ity,  behavior   towards   chemical   agents,    power   of   conducting 
heat   and    electricity   and   in   various    other  respects,    they  all 
agree   in  this,  that,   on  being  strongly  heated  in  presence  of 
oxygen,   they  unite  with  it  and  form  the  same  compound,  an 
oxide  of  carbon  (CO2). 

175.  Diamond.  —  The  diamond  is  pure  or  nearly  pure  carbon 
and  occurs  in  nature  in  octahedral  crystals.     Its  rarity  and  its 
high  refractive  power  as  regards  light,  together  with  the  diffi- 
culty with  which  it  is  worked,  make  it  the  most  precious  of 
gems.     It  is  the  hardest  known  substance.     The  diamond  has 
not  as  yet  been  produced  artificially. 

The  diamond  is  not  attacked  by  the  strongest  acids  or  alka- 
10 


HO  GRAPHITE.  —  GAS-CARBON.  [§  176. 

lies,  not  even  by  fluorhydric  acid  ;  nor  is  it  acted  upon  by  any 
of  the  non-metallic  elements,  with  the  exception  of  oxygen  at 
high  temperatures.  At  the  ordinary  temperature  of  the  air, 
diamond  undergoes  no  appreciable  change.  Out  of  contact 
with  the  air,  or  in  an  atmosphere  which  has  no  chemical 
action  upon  it,  it  suffers  no  alteration  at  the  highest  furnace 
heat ;  heated  white-hot  between  the  charcoal  points  of  a  power- 
ful galvanic  battery,  it  softens  and  swells  up,  forming  a  black 
brittle  mass  like  coke ;  heated  in  oxygen  gas,  it  burns  to 
carbonic  acid  (CO2). 

176.  Graphite  or  Plumbago,  sometimes  called  "  black-lead," 
is  familiarly  known  as  the  material  of  common  "  lead  pencils." 
It  is  found  as  a  mineral  in  nature  in  various  localities.     It 
occurs   both  in  the  form    of   crystals   and   in   the   amorphous, 
massive  state.     In  both  forms  it  is  always  opaque,  of  a  black  or 
lead-gray  color  and  metallic  lustre. 

Graphite  is  very  friable  ;  when  rubbed  upon  paper,  it  leaves 
a  black  shining  mark,  whence  its  use  for  pencils.  Amorphous 
graphite  is  so  soft  and  unctuous  to  the  touch  that  it  is  often 
used  as  a  lubricant  for  diminishing  the  friction  of  machinery  : 
but  in  spite  of  this  seeming  softness,  the  particles  of  which 
the  masses  of  graphite  are  composed  are  extremely  hard ;  they 
rapidly  wear  out  the  saws  employed  to  cut  these  masses.  In 
the  air,  at  ordinary  temperatures,  graphite  undergoes  no 
change ;  hence  its  use  for  covering  iron  articles  to  prevent 
their  rusting.  By  virtue  of  its  greasy,  adhesive  quality,  it  is 
easy  to  cover  iron  with  a  thin,  lustrous  layer  or  varnish  of  it ; 
the  common  stove-polishes,  for  example,  are  composed  of  pow- 
dered graphite. 

177.  Gas-Carbon,  —  An    interesting    sub-variety   of    carbon 
somewhat  similar  to  graphite,  and  standing,  as  it  were,  between 
it  and  the  ordinary  modification  of  carbon,   is  obtained  from 
the  retorts  in  which  common  illuminating  gas  is  manufactured. 
It  is  known  as  "  gas-carbon,"   or  "  carbon  of  the  gas-retorts," 
and  results  from  the  burning  on  of  drops  of  tar  upon  the  in- 
terior walls  of  the  retort,  and  the  long-continued  heating  of  the 
crust  thus  formed, 


Fig,  35. 


§178.]    COKE.  —  A  XTH&A  CITE  A  ND  &1 TUMI NO  VS  CO  A  L.     \\\ 

Gas-carbon  is  very  hard,  compact  and  dense  :  it  has  a 
metallic  lustre,  and  conducts  electricity  like  a  metal.  On 
account  of  its  high  conducting  power,  it  is  employed  in  the 
manufacture  of  galvanic  batteries  and  of  pencils  for  the  electric 
lamp. 

178.  Coke  and  Anthracite  Coal  are  impure  sub- varieties  of 
carbon  which,  from  the  chemical  point  of  view,  may  be  classed 
either  with  graphite  or  charcoal,  or  better  between  the  two. 
They  are  less  like  graphite,  however,  than  gas-carbon  is.  Coke 
is  the  residue  resulting  from  the  destructive  distillation  of  soft 
or  bituminous  coal. 

Exp.  65.  —  Put  into  a  tube  of 
hard  glass,  No.  1,  12  or  15  c.  m.  in 
length,  enough  bituminous  coal,  in 
coarse  powder,  to  fill  one-third  of 
the  tube.  Fit  to  this  ignition-tube 
a  large  delivery-tube  of  glass,  No.  4, 
and  support  the  apparatus  upon  the 
iron  stand,  as  shown  in  the  figure. 
Heat  the  coal  in  the  ignition-tube, 
and  collect  in  bottles  the  gas  which 
will  be  evolved.  The  gas  will  burn  with  a  yellow  flame  on  the  appli- 
cation of  a  match.  This  gas  is,  in  the  main,  a  mixture  of  several  com- 
pounds of  carbon  and  hydrogen ;  for  the  present,  it  may  be  regarded 
as  carburetted  hydrogen.  It  is,  in  fact,  ordinary  illuminating  gas. 

As  soon  as  gas  ceases  to  be  given  off  from  the  coal,  take  the  end  of 
the  delivery-tube  out  of  the  water,  and  when  the  ignition-tube  has" 
become  cold,  break  it,  and  examine  the  coke  which  it  contains.  The 
coke  used  for  domestic  purposes  is  obtained  as  an  incidental  product 
in  the  manufacture  of  illuminating  gas. 

Bituminous  coal  is  a  substance  of  vegetable  orgin,  which  ap- 
pears to  have  been  formed  from  plants  by  a  process  of  slow  decay 
going  on  without  access  of  air  and  under  the  influence  of  heat,  mois- 
ture and  great  pressure.  Like  vegetable  matter  in  general,  it  is 
composed  of  carbon  and  hydrogen,  together  with  small  proportions 
of  oxygen  and  nitrogen,  and  a  certain  quantity  of  earthy  and  saline 
substances,  commonly  spoken  of  as  inorganic  matter.  On  being 
heated  in  the  air,  it  burns  away  almost  completely  after  a  while,  leav- 
ing nothing  but  the  inorganic  components  as  ashes.  But  when  heated 


112  CHARCOAL.  — LAMP-BLACK.  [§  179. 

out  of  contact  with  the  air,  that  is  to  say,  when  subjected  to  destruc- 
tive distillation,  as  in  Exp.  65,  the  volatile  hydrogen  is  all  driven  off 
in  combination  with  some  carbon,  either  as  gas  or  as  a  tarry  liquid, 
and  the  residue,  or  coke,  contains  only  carbon  contaminated  with 
the  inorganic  matters  originally  present  in  the  coal. 

In  Europe,  where  anthracite  is  lacking,  immense  quantities  of  coke 
are  prepared  for  metallurgical  uses,  the  gas  resulting  from  the  decom- 
position of  the  coal  being  usually  thrown  away. 

Anthracite  is  supposed  to  have  been  formed,  like  bituminous 
coal,  from  the  slow  decay  of  vegetable  matter,  and  then  to  have  been 
subjected  to  some  sort  of  natural  distillation  by  which  it  has  been  de- 
prived of  nearly  all  the  hydrogen,  nitrogen  and  oxygen  of  the  original 
wood.  It  is  thus  a  coke  formed  by  natural  agencies. 

179.  Both  coke  and  anthracite  are  hard  and  lustrous.     As 
compared  with  charcoal,  they  are  rather  difficult  of  combustion. 
Both   anthracite  and  coke,   the  latter  in  spite   of  its  porosity, 
conduct  heat  readily,  as  compared  with    charcoal ;   hence   one 
reason  of  the  difficulty  of  kindling  them.     In  building  a  char- 
coal fire,  the  heat  evolved  by  the  combustion  of  the  kindling 
material  is  almost  all  retained  by  the  portions  of  charcoal  im- 
mediately in  contact  with  the  kindling  agent,  but  in  the  case  of 
coke  or  anthracite,  a  large  proportion  of  this  heat  is  conducted 
off  and  diffused  throughout  the  heap  of  fuel,  so  that  no  portion 
of  the  fuel  can  at  once  become  very  hot. 

180.  Charcoal   or  Lamp-black    is    commonly  taken  as  the 
representative  of  the  third  or  amorphous  modification  of  carbon. 
This  kind  of  carbon  can  be  obtained  in  a  state   of   tolerable 
purity,  either  by  heating  in  a  close  vessel  sugar,  starch  or  some 
other  organic  substance  which  contains  no  inorganic  constituents, 
or  by  burning  oil  of  turpentine  in  a  quantity  of  air  insufficient 
for  its  complete  combustion. 

Charcoal  can  be  obtained  also  by  distilling  wood  in  retorts  in 
the  same  way  that  we  have  seen  that  coke  can  be  procured  from 
bituminous  coal.  (See  Exp.  65.) 

Exp.  66.  —  Provide  an  ignition-tube  and  a  delivery-tube  similar 
to  those  employed  in  Exp.  65.  Fill  the  ignition-tube  with  shavings  or 
small  fragments  of  wood,  arrange  the  apparatus  as  before  and  light 


§  180.1  PREPARATION  OF  CHARCOAL.  113 

the  gas-lamp.  Collect  in  bottles  the  gas  which  is  given  off  from 
the  wood  and  test  it  as  to  its  inflammability  by  applying  a  lighted 
match.  After  the  flow  of  gas  has  ceased,  remove  the  end  of  the 
delivery-tube  from  the  water,  plug  it  so  that  no  air  can  enter  the 
ignition-tube  and  lay  the  apparatus  aside  until  it  has  become  cold. 
Finally,  remove  the  cork  from  the  ignition-tube  and  take  out  the 
charcoal  which  is  contained  in  it.  Heat  a  portion  of  this  charcoal 
upon  platinum  foil  and  observe  the  manner  in  which  it  burns  :  it  will 
illustrate  the  fact  that  solid  substances  which  are  incapable  of  evolv- 
ing volatile  or  gaseous  matter  do  not  burn  with  flame,  —  they  merely 
glow. 

For  use  in  the  arts  charcoal  is  sometimes  prepared  by 
distilling  the  wood  in  retorts,  but  more  generally  by  burning 
the  wood  with  little  access  of  air.  Logs  of  wood  are  piled  up 
into  a  large  mound  or  stack  around  a  central  aperture,  which 
subsequently  serves  as  a  temporary  chimney  and  also  for 
the  introduction  of  burning  substances  for  firing  the  heap. 
The  finished  heap  is  covered  with  chips,  leaves,  sods  and  a 
mixture  of  moistened  earth  and  charcoal  dust,  a  number  of 
apertures  being  left  open  around  the  bottom  of  the  heap 
for  the  admission  of  air  and  .the  escape  of  the  products  of  dis- 
tillation and  combustion.  The  heap  is  kindled  at  the  cen- 
tre and  burns  dur-  Fi&'  36< 
ing  several  weeks. 
When  the  process 
is  judged  to  be 
complete,  all  the 
openings  are  care- 
fully stopped  in 
order  to  suffocate 
the  fire,  and  the 
heap  is  then  left 
to  itself  until  cold.  The  charcoal  retains  the  form  of  the 
wood,  —  the  shape  of  the  knots  and  the  annual  rings  of  the 
wood  being  still  perceptible  in  it,  —  but  it  occupies  a  much 
smaller  volume  than  the  wood  :  generally  its  bulk  does  not 
amount  to  more  than  three-fourths  of  that  of  the  wood,  and 
10* 


114  LAMP-BLACK.  [§  181. 

its  weight  never  exceeds  one-fourth  the  weight  of  the  wood. 
Sometimes  kilns  built  of  brick  are  used  instead  of  the  rude 
heaps  here  described. 

Where  charcoal  is  prepared  b,y  distilling  wood  in  retorts,  the 
liquid  products  of  distillation,  namely,  tar  and  acetic  acid 
("  pyroligneous  acid  "),  are  saved  and  utilized. 

181.  Lamp-black.  —  Upon  the  large  scale,  lamp-black  is 
manufactured  by  heating  organic  matters,  such  as  tar,  resin 
or  pine  knots,  which  contain  volatile  ingredients  very  rich  in 
carbon,  until  vapors  are  disengaged,  and  then  burning  these 
vapors  in  a  current  of  air  insufficient  for  their  complete  com- 
bustion. The  vapors  consist  of  compounds  of  carbon  and 
.hydrogen,  and  the  supply  of  air  being  insufficient  to  consume 
both  hydrogen  and  carbon,  a  large  portion  of  the  carbon  of 
the  combustible  does  not  burn,  but  is  deposited  as  a  very  line 
powder  precisely  similar  to  that  which  constitutes  the  black 
portion  of  common  smoke.  Lamp-black  finds  important  ap- 
plications in  the  arts  as  a  pigment  and  as  the  chief  ingredient 
of  printers'  ink. 

.  Exp.  67 .  —  Fill  an  ordinary  spirit-lamp  (Appendix,  §  5)  with  oil 
of  turpentine,  light  the  wick  and  place  over  it  an  inverted  wide- 
mouthed  bottle  of  the  capacity  of  a  litre  or  more,  one  edge  of  the 
mouth  of  the  bottle  being  propped  up  on  a  small  block  of  wood,  so 
that  some  air  may  enter  the  bottle.  As  the  supply  of  air  is  insuffi- 
cient for  the  perfect  combustion  of  the  oil  of  turpentine,  a  quantity 
of  lamp-black  will  separate  and  be  deposited  upon  the  sides  of  the 
bottle. 

Hydrogen  kindles  at  a  lower  temperature  than  carbon,  hence 
if  the  flame  of  a  burning  compound  of  carbon  and  hydrogen  be 
cooled  down  below  the  temperature  at  which  carbon  takes  fire, 
lamp-black  will  be  formed,  even  if  there  be  present  an  abundant 
supply  of  air. 

Exp.  68.  —  Press  down  upon  the  flame  of  an  oil-lamp  or  candle 
an  iron  spoon  or  a  porcelain  plate  in  such  manner  that  the  flame  shall 
be  almost,  but  not  quite  extinguished.  The  solid  body  not  only  ob- 


§  182.]  CHARCOAL  A   REDUCING  AGENT.  115 

structs'  the  draught  of  air,  and  thereby  interferes  with  the  act  of 
combustion,  but  it  also  cools  the  flame  by  Fig.  37. 

actually  conducting  away  part  of  its  heat ; 
the  temperature  is  thus  reduced  to  below  the 
kindling-point  of  carbon,  and  a  quantity  of 
lamp-black  remains  unconsurned  and  adher- 
ing to  the  spoon  or  plate.  The  deposit  of 
lamp-black  is,  of  course,  comparable  with 
the  spots  of  arsenic  and  antimony,  alluded  to 
in  §§  157,  166,  as  being  obtained  upon  porce- 
lain, as  products  of  the  incomplete  combus- 
tion of  the  hydrogen  compounds  of  these 
elements. 

182.  In  all  its  varieties,  charcoal  is  a  very  important  chemi- 
cal agent,  chiefly  because  of  the  readiness  and  energy  with 
which  it  combines  with  oxygen  at  high  temperatures.  It  might 
almost  be  said  that  the  art  of  metallurgy,  as  it  now  exists,  is 
based  upon  the  affinity  of  carbon  for  oxygen. 

Exp.  69.  — -  Mix  two  and  a  half  grammes  of  copper  oxide  with  a 
quarter  of  a  gramme  of  powdered  charcoal ;  place  a  portion  of  the 
mixture  in  an  ignition-tube  made  of  No.  3  glass,  and  heat  it  strongly 
in  the  gas-lamp.  The  charcoal  will  unite  with  the  oxygen  of  the 
copper  oxide,  and  the  compound  thus  formed  will  escape  in  the  form 
of  gas,  while  metallic  confer  will  remain  in  the  tube. 

This  experiment  is  analogous  to  Exp.  62,  where  arsenious  acid  was 
reduced  by  means  of  charcoal.  Both  experiments  are  typical  of  the 
manner  in  which  hot  charcoal  acts  upon  metallic  oxides.  At  a  white 
heat  it  removes  oxygen  from  its  combinations  with  some  elements 
which  hold  it  with  great  force,  such  as  the  oxicles  of  sodium  and 
potassium,  phosphoric  acid  and  water.  If  a  current  of  steam  be 
passed  over  red-hot  charcoal,  the  steam  is  decomposed  ;  the  hydrogen 
is  set  free,  and  the  oxygen  of  the  steam  combines  with  a  portion  of 
the  carbon  to  form  carbon  protoxide  (CO),  an  inflammable  gas. 
The  reaction  which  occurs  may  be  formulated  as  follows  :  C  -f-  H2O 
=  CO  -f  2  H. 

The  deoxidizing  power  of  charcoal,  thus  illustrated,  is 
exhibited  only  at  high  temperatures.  At  the  ordinary  tem- 
perature of  the  air,  the  chemical  energy  of  charcoal  is  exceed- 


116  PROPERTIES  OF  CHARCOAL.  f§  133 

ingly  feeble.  Charcoal  is,  in  fact,  one  of  the  most  durable  of 
substances.  Specimens  of  it  have  been  found  at  Pompeii  and 
upon  Egyptian  mummies,  to  all  appearance  as  fresh  as  if  just 
prepared  :  the  action  of  the  air  continued  through  centuries 
has  exerted  no  appreciable  influence  upon  it.  Fence-posts 
which  are  sunk  for  a  certain  distance  into  the  ground  are  often 
charred  on  the  outside,  and  thus  rendered  more  durable. 

183.  A  physical   property  of  charcoal,  which   is   of  great 
practical    importance,    is    its    power   of    absorbing    and    con- 
densing within  its  pores  a  great  variety  of  gases  and  vapors. 
Freshly-burned    charcoal  exposed  to  damp  air,   in  a  cellar  for 
instance,  will  gain  10  or  12  per  cent  in  weight  in  the  course  of 
a  single  day. 

Exp.  70.  —  Take  from  the  fire  a  piece  of  charcoal  which  has 
been  heated  to  full  redness  for  some  time ;  thrust  it  under  water  so 
that  it  may  be  suddenly  cooled,  and  observe  that  it  sinks  in  the  water 
and  that  few  or  no  bubbles  of  gas  escape  from  its  pores. 

Take  another  piece  of  charcoal  which  has  long  been  exposed  to  the 
air  and  has  not  recently  been  heated,  attach  to  it  a  quantity  of  sheet- 
lead  sufficient  to  sink  it  in  water,  and  immerse  the  whole  in  a  large 
beaker-glass  two-thirds  full  of  hot  water.  The  mobile  water  will  im- 
mediately enter  the  pores  of  the  charcoal,  and  a  portion  of  the  air 
which  had  previously  been  absorbed  by  these  pores  will  be  driven  out, 
and  can  be  seen  escaping  in  bubbles  through  the  water,  chiefly  from 
the  broken  ends  of  the  coaL 

To  the  presence  of  air  and  aqueous  vapor,  which  has  been 
thus  absorbed,  is  to  be  attributed  the  snapping  and  crackling 
of  old  charcoal  when  it  is  thrown  upon  a  hot  fire. 

Different  gases  are  absorbed  by  charcoal  in  very  different  propor- 
tions :  thus  a  cubic  centimetre  of  dry,  compact  charcoal,  such  as  that 
from  boxwood,  will  absorb  as  much  as  90  c.  c.  of  ammonia-gas  in  the 
course  of  24  hours  ;  while  in  the  same  time  it  will  absorb  only  35  c.  c. 
of  carbonic  acid  and  only  2  c.  c.  of  hydrogen. 

184.  Charcoal  is  much  employed  as  a  disinfecting  agent. 
It  is  capable  of  removing  many  offensive  odors  from  the  air, 


§  185.1  PROPERTIES  OF  CHARCOAL.  117 

such,  for  example,  as  the  fetid  products  given  off  during  the 
putrefaction  of  animal  and  vegetable  substances.  Animal  mat- 
ter in  an  advanced  stage  of  putrefaction  loses  all  offensive  odor 
when  covered  with  a  layer  of  charcoal,  and  the  flesh  of  a  dead 
animal  buried  beneath  a  thin  layer  of  charcoal  will  gradually 
waste  away  and  be  consumed  without  exhaling  any  unpleasant 
smell. 

Exp.  71.  —  Place  a  small  quantity  of  powdered  charcoal  in  a 
bottle  containing  hydrogen  sulphide  gas,  and  shake  the  bottle.  The 
odor  of  the  hydrogen  sulphide  will  quickly  disappear.  In  the  same 
way,  an  aqueous  solution  of  hydrogen  sulphide  (Exp.  48)  can  be  de- 
odorized by  filtering  it  through  a  layer  of  charcoal. 

In  all  these  cases,  the  use  of  charcoal  as  a  disinfectant  depends 
not  merely  upon  its  mechanical  ability  to  absorb  offensive  gases,  but 
also  and  mainly  upon  the  fact  that  the  absorbed  gases  are  chemically 
destroyed  within  the  pores  of  the  coal  by  the  oxygen  which  is  sucked 
into  these  spaces  from  the  air.  The  purifying  action  depends  upon 
oxidation,  upon  the  burning  up  of  the  offensive  gases.  The  charcoal 
is  in  no  sense  an  antiseptic  or  preservative  agent  proper  to  prevent 
decay  ;  on  the  contrary,  it  actually  hastens  the  destruction  of  putres- 
cible  organic  matters.  Under  ordinary  circumstances,  the  pores  of 
charcoal  contain  more  or  less  oxygen  which  has  been  absorbed  from 
the  air,  and  any  new  gas  which  is  dragged  in  is  forced  into  intimate 
contact  with  this  oxygen,  If  the  new  gas  is  one  on  which  oxygen  can 
act,  it  is  destroyed  ;  and  as  fresh  portions  of  the  gas  are  absorbed  by 
the  charcoal,  additional  quantities  of  oxygen  are  also  absorbed,  so  that 
the  action  may  go  on  for  a  long  time.  A  great  merit  of  charcoal  as  a 
disinfectant  is,  that  it  constantly  draws  in  to  destruction  the  offensive 
matters  around  it ;  pans  of  charcoal  placed  about  a  room,  —  the 
wards  of  a  hospital,  for  example,  —  the  air  of  which  is  offensive, 
soon  remove  the  unpleasant  smell. 

185.  Charcoal  not  only  destroys  odors,  but  it  removes  colors 
as  well,  and  for  this  purpose  it  has  long  been  employed  in  the 
purification  of  sugar  and  of  many  chemical  and  pharmaceu- 
tical preparations.  Almost  any  coloring  matter  can  be  re- 
moved from  a  solution  by  filtering  the  liquid  through  a  layer 
of  charcoal. 


118  CHARCOAL   DECOLORIZES.  [§  186 

Exp.  72.  — Provide  four  small  bottles  of  the   capacity  of  100  or 
200  c.  c.,  and  place  in  each  of  them  a  table-spoonful  of  bone-black 
Fig.  38.  (§  186)  ;  into  the  first  bot- 

tle pour  a  quantity  of  the 
blue  compound  of  iodine 
and  starch  obtained  in 
Exp.  39  ;  into  the  second, 
a  decoction  of  cochineal ; 
into  the  third,  a  dilute 
solution  of  soluble  indigo 
blue  ;  into  the  fourth  a 
solution  of  blue  litmus, 
of  logwood,  or  indeed  ol 
almost  any  other  vegetable 
coloring  matter  ;  enough 
of  the  solution  being  taken 
in  each  instance  to  nearly  fill  the  bottle.  Cork  the  bottles  and  shake 
them  violently,  then  pour  the  contents  of  each  upon  a  filter  (see  Ap- 
pendix, §  15) ,  and  observe  that  the  filtrate  is  in  each  instance  color- 
less, or  nearly  so.  In  case  the  first  portions  of  the  filtrate  happen  to 
come  through  colored,  they  may  be  poured  back  upon  the  filter  and 
allowed  to  again  pass  through  the  coal. 

In  the  purification  of  brown  sugar,  the  coloring  matters  are  removed 
in  a  manner  similar  to  the  foregoing,  the  colored  sirup  being  filtered 
through  layers  of  bone-black.  Besides  coloring  matters,  charcoal  can 
absorb  many  other  substances  :  sulphate  of  quinine,  for  example,  is 
removed  from  its  solutions,  to  a  very  considerable  extent,  by  charcoal, 
and  the  same  remark  applies,  with  perhaps  still  more  force,  to  strych- 
nine. The  bitter  principle  of  the  hop,  "  lupulin,"  may  be  entirely 
removed  from  ale  by  filtering  the  latter  through  bone-black. 

In  all  these  cases  where  coloring  matters,  and  the  like,  are  removed 
from  solutions,  the  action  of  the  coal  appears  to  depend  in  the  main 
directly  upon  the  physical  property  of  adhesion ;  the  subsequent 
oxidizing  action  being  here  far  less  clearly  marked  than  in  the 
instances  previously  studied  (§  184)  where  gases  are  acted  upon. 
Much  of  the  absorbed  color  or  other  matter  will  usually  be  found 
attached  to  the  surfaces  of  the  coal,  undecomposed  and  unaltered. 

186.  As  obtained  from  different  sources,  charcoal  exhibits 
very  different  degrees  of  decolorizing  power ;  but  of  the  varie- 


§  188.]  CARBONIC  ANHYDRIDE.  \\§ 

ties  commonly  met  with  and  to  be  procured  in  commerce,  bone- 
black  is  the  most  efficient.  Bone-black  is  prepared  for  the  use 
of  sugar-refiners,  by  subjecting  bones  to  destructive  distillation 
in  large  iron  cylinders  and  carefully  cooling  the  charcoal  out  of 
contact  with  the  air.  As  dry  bones  contain  about  66  per  cent 
of  mineral  matter,  the  charcoal  thus  obtained  is  left  in  an 
exceedingly  porous  condition,  distributed  over  and  among  the 
particles  of  the  mineral  matter. 

187.  Compounds  of  Carbon  and  Oxygen.  —  There  are  two 
of  these  compounds,  —  Carbonic  anhydride  (CO2)  and  carbon 
protoxide  (CO). 

188.  Carbonic   anhydride,  commonly  called  carbonic  acid 

(CO2),  is  always  formed  when  carbon  or  any  of  its  compounds  is 
burned  in  an  excess  of  air  or  of  oxygen  gas,  or  in  contact  with 
substances,  gaseous,  liquid  or  solid,  which  are  rich  in  oxygen, 
and  yield  it  readily  to  other  bodies. 

Exp.  73. —  Place  a  live  coal  (charcoal)  upon  a  deflagrating  spoon, 
and  thrust  it  into  a  bottle  full  of  air,  or,  better,  oxygen  gas  :  when 
the  coal  has  ceased  to  glow,  pour  into  the  bottle  some  lime-water,  — 
a  solution  of  common  slaked  lime  in  water,  —  and  shake  the  bottle. 
The  liquid  will  become  milky  and  turbid,  and,  when  left  at  rest,  will 
deposit  a  white  powder  (calcium  carbonate).  The  presence  of  carbonic 
acid  can  readily  be  detected  by  means  of  lime-water,  since  this  insolu- 
ble precipitate  of  calcium  carbonate  is  formed  when  the  two  sub- 
stances are  brought  together. 

From  the  formulae  of  the  class  of  bodies  known  as  carbonates 
(sodium  carbonate  =  Na2CO3),  we  should  infer 'the  existence  of  a 
carbonic  acid  of  the  formula  H2CO3.  Carbonic  anhydride  does 
dissolve  in  water,  and  the  solution  has  a  slightly  acid  reaction  :  it  is, 
however,  doubtful  if  a  definite  compound  is  formed.  The  term  car- 
bonic acid  has,  however,  been  so  long  applied  to  the  oxide  of  carbon, 
CO2 ,  and  the  term  has  such  a  foothold  in  our  language  and  literature, 
that  it  will  be  used  in  this  chapter  in  its  popular  sense. 

Exp  74.  —  As  was  just  now  said,  carbonic  acid  may  be  produced 
also  by  heating  carbon  in  contact  with  solid  bodies  which  contain 
oxygen,  such,  for  example,  as  the  red  oxide  of  mercury.  Mix  11 
grins,  of  red  oxide  of  mercury  with  0.33  grm.  of  charcoal  ;  place  the 


120  CARBONIC  ACID.— CARBONATES.  [§  189. 

mixture  in  an  ignition-tube  arranged  as  in  Figure  35  ;  heat  the  tube 
and  collect  over  water  the  gas  which  is  evolved.  Test  the  product 
with  lime-water,  as  in  Exp.  73.  The  reaction  between  the  charcoal 
and  the  mercury  oxide  may  be  written  as  follows  :  — 

2  HgO  -f  C  =  C02  -|-  2  Hg. 

The  metallic  mercury  set  free  condenses  in  droplets  upon  the  cold 
upper  portions  of  the  ignition-tube.  Here,  again,  as  in  Exps.  62  and 
69,  the  metallic  oxide  is  reduced  by  the  charcoal. 
^  189.  Carbonic  acid  may  readily  be  obtained  from  certain 
compounds  called  carbonates,  several  of  which  are  abundant 
minerals.  Common  chalk,  marble  and  limestone,  for  example, 
are  composed  of  calcium  carbonate;  and  carbonic  acid  can 
readily  be  obtained  by  strongly  heating  them,  or  by  subjecting 
them  to  the  action  of  strong  acids. 

Exp.  75.  —  In  a  gas-bottle  of  500  or  600  c.  c.  capacity,  arranged 
precisely  as  for  generating  hydrogen  (see  Exp.  11,  §  35),  place  10  or  12 
Pig.  39.  grins,  of  chalk  or  marble  in 

small  lumps  ;  cover  the  chalk 
with  water,  and  pour  in 
through  the  thistle-tube  con- 
centrated chlorhydric  acid, 
by  small  portions,  in  such 
quantity  as  shall  insure  a 
continuous  and  equable  evo- 
lution of  gas.  Collect  sev- 
eral bottles  of  the  gas  over 
water,  then  replace  the  an- 
terior portion  of  the  deliv- 
ery-tube with  a  straight  tube 
and  collect  one  or  two  bottles  of  the  gas  by  displacement  ;  carbonic' 
acid  gas  is  half  as  heavy  again  as  air.  The  reaction  between  the 
calcium  carbonate  and  the  chlorhydric  acid  may  be  thus  formulated  : 
CaC03  -f-  2  HC1  =  CaCl2  -f  H2O  -f  CO2. 

190.  At  the  ordinary  atmospheric  temperature  and  pressure, 
carbonic  acid  is  a  transparent,  colorless  gas,  of  a  slightly  acid 
smell  and  taste.  It  is  incombustible,  being  already  the  product 
of  the  complete  combustion  of  carbon,  and  is,  moreover,  inca- 


§  192.]  PROPERTIES  OF  CARBONIC  ACID.  121 

pable  of  supporting  the  combustion  of  most  other  bodies  :  it  is 
also  incapable  of  supporting  animal  life. 

Exp.  76.  —  Thrust  into  a  bottle  of  the  gas,  obtained  in  Exp.  75, 
a  lighted  candle,  or,  better,  a  large  flame  of  alcohol  burning  upon  a 
tuft  of  cotton  ;  in  either  case  the  flame  will  be  instantly  extinguished. 

191.  The  specific  gravity  of  carbonic  acid  is  22  ;  being  thus 
1.53  times  heavier  than  air,  it  can  be  poured  from  one  vessel  to 
another  almost  as  readily  as  if  it  were  water. 

Exp.  77. —  From  a  large  bottle  or  other 
vessel  full  of  the  gas-,  pour  a  quantity  of  car- 
bonic acid  upon  the  flame  of  a  lamp  or  can- 
dle ;  that  is  to  say,  hold  the  mouth  of  the 
open  bottle  of  carbonic  acid  obliquely  over 
the  candle  flame,  so  that  the  gas  shall  fall 
like  water  upon  it  :  the  flame  will  immedi- 
ately be  extinguished. 

Carbonic    acid    can  be   obtained    in    the 
liquid  state  by  subjecting  the  gas  to  pressure.     It  can  also  be  obtained 
in  a  solid  snow-like  state  by  exposing  the  liquid  to  cold. 

192.  Carbonic  acid  gas  is  soluble  in  water  to  a  considerable 
extent.     One  measure  of  water  at  the  ordinary  temperature  and 
pressure,  will  dissolve  one  measure  of  carbonic  acid  gas,  but  its 
solubility  increases  if  the  pressure  be  increased. 

Exp.  78.  —  Into  a  long-necked  flask  or  phial  filled  with  carbonic 
acid,  pour  a  quantity  of  water,  close  the  bottle  with  the  finger  and 
shake  it ;  immerse  the  mouth  of  the  bottle  in  water,  and  remove  the 
finger  ;  water  will  rush  into  the  bottle  to  supply  the  place  of  the  gas 
which  has  been  dissolved.  Again  place  the  finger  upon  the  mouth  of 
the  bottle,  shake  the  bottle  as  before  and  subsequently  open  it  beneath 
the  surface  of  the  water  ;  a  fresh  portion  of  water  will  flow  into  the 
bottle  to  supply  the  new  vacuum  ;  in  this  way,  by  repeated  agitation 
with  water,  all  of  the  carbonic  acid  in  the  bottle  can  be  absorbed. 
• 

When  subjected  to  increased  pressure,  carbonic  acid  gas  dis- 
solves in  water  much  more  abundantly  than  at  the   ordinary 
pressure  of  the  air.     Water  thus  surcharged  with  carbonic  acid 
has  an  agreeable,  acid,  pungent  taste,  and  effervesces  briskly 
11 


122  PRODUCTION  OF  CARBONIC  ACID.  [§  193, 

when  the  compression  is  suddenly  removed,  as  when  the  liquid 
is  allowed  to  flow  out  into  the  air ;  such  carbonic  acid  water,  or 
"  mineral  water,"  as  it  is  then  called,  flows  from  the  earth  in 
many  localities,  as  at  Seltzer  and  Saratoga  :  it  is  also  prepared 
artificially,  in  large  quantities,  and  sold  as  a  beverage  under  the 
meaningless  name  of  soda-water.  The  effervescent  qualities  of 
fermented  liquors,  such  as  cider,  champagne  and  beer,  are,  in  like 
manner,  dependent  upon  the  presence  of  compressed  carbonic 
acid  gas. 

193.  Carbonic  acid  is  produced,  not  only  in  the  actual  com- 
bustion of  all  substances  which  contain  carbon,  but  also  during 
the  decay  and  putrefaction  of  all  animal  and  vegetable  sub- 
stances.    During  fermentation  it  is  evolved  in  large  quantities, 
and  it  is  continually  given  oft'  during  the  respiration  of  ani- 
mals. 

Exp.  79.  —  Dissolve  10  grms.  of  honey  or  molasses  in  100  c.  c. 
of  water  ;  fill  a  large  test-tube  with  the  mixture  and  add  to  it  a  few 
drops  of  bakers'  or  brewers'  yeast  ;  close  the  open  mouth  of  the  test- 
tube  with  the  thumb,  and  invert  it  in  a  small  saucer  or  porcelain 
capsule  filled  with  the  diluted  sirup.  Place  the  saucer  and  tube,  with 
their  contents,  in  a  warm  place,  having  a  temperature  of  about  20° 
or  30°,  and  leave  them  there  during  24  hours.  In  a  short  time  fer- 
mentation sets  in,  and  the  sugar  of  the  sirup  is  gradually  converted 
into  alcohol  and  carbonic  acid. 

C6H1206  •=  2  C2HG0  -f  2  C02. 

Sugar.  Alcohol. 

The  carbonic  acid  thus  formed  rises  in  minute  bubbles,  causing  a 
gentle  effervescence  in  the  liquid,  and  collects  in  the  upper  part  of 
the  tube,  while  the  alcohol  remains  dissolved  in  the  liquid. 

Exp.  80.  —  Provide  two  test-glasses  or  small  bottles  ;  place  in 
each  15  or  20  c.  c.  of  lime-water  ;  through  a  glass  tube,  blow  into  the 
lime-water  of  one  of  the  bottles  air  coming  from  the  lungs.  By 
means  of  bellows,  to  the  nozzle  of  which  a  gas-delivery  tube  has  been 
attached,  force  through  the  lime-water  of  the  Second  bottle  a  quantity 
of  fresh  air.  The  clear  liquid  of  the  first  bottle  will  quickly  become 
turbid  through  deposition  of  calcium  carbonate,  while  the  lime-water 
of  the  second  bottle  will  remain  clear  for  a  long  while. 

194.  Carbonic   acid   is  an  exceedingly   weak  acid  ;   it  fails  to 


§  196.1  CARBON  PROTOXIDE.  123 

neutralize  (§  48)  completely  the  causticity  of  hydrates,  such  as 
those  of  the  alkaline  metals  ;  the  normal  carbonate  of  sodium,  for 
example,  is  decidedly  alkaline  in  its  reaction  and  properties.  Al- 
most all  the  carbonates  are  readily  decomposed  by  acids,  —  even  by 
very  weak  acids,  —  with  an  effervescence  caused  by  the  escape  of 
carbonic  acid  :  many,  among  them  calcium  carbonate,  are  decomposed 
by  heat. 

Carbonic  acid  is  bibasic  (§  134)  like  sulphuric  acid  ;  thus  there 
exist  a  sodium  carbonate,  Na2CO3,  and  a  hydrogen  sodium  carbonate, 
HNaCO3  ("  bicarbonate  of  soda  "). 

195.  Carbon  Protoxide  (CO),  called  also  carbonic  oxide, 

may  be  prepared  by  passing  carbonic  acid  over  hot  charcoal 
(C  -f-  CO2  =  2  CO)  or  by  heating  the  oxides  of  almost  any  of 
the  metals  with  an  excess  of  charcoal.  The  gas  is,  however, 
contaminated  with  some  carbonic  acid.  It  may  be  prepared  pure 
as  follows  :  — 

Exp.  81. — In  a  flask  of  about  250  c.  c.  capacity,  provided  with  a 
delivery-tube  and  with  a  safety-tube  (Fig.  41),  heat  gently  a  mixture 
of  5  grins,  of  finely-powdered  potassium  ferrocyanide  (yellow  prus- 
siate  of  potash)  and  40  or  50  grms.  of  strong  sulphuric  acid.  Collect 
the  gas  over  water  and  test  it  as  to  its  inflammability.  Thrust  also  a 
lighted  splinter  into  the  gas  and  observe  that  it  will  be  extinguished. 
The  reactions  which  occur  between  the  chemicals  employed  will  be 
explained  in  a  subsequent  section  (see  §  387). 

196.  Carbon  protoxide  is  a  transparent,  colorless  gas,  hav- 
ing little,  if  any,  odor ;  it  may  be  liquefied,  but  with  great  diffi- 
culty.    The  gas  is  somewhat  lighter  than  air,  its  specific  gravity 
being  14,  while  that  of  air  is  14.5.     It  is.  but  little  soluble  in 
water,  and  may  be  collected  over  water  without  much  loss.     It 
extinguishes  combustion  just  as  hydrogen  does,  and  destroys 
animal   life.     Unlike  hydrogen  and  nitrogen,  however,  it  is  a 
true  poison.     It  destroys  life,  not  negatively  by  mere  suffoca- 
tion or  exclusion  of  oxygen,  but  by  direct  noxious  action.     It  is 
the  presence  of  this  gas  which  occasions  the  peculiar  sensation 
of  oppression  and  headache  which  is  experienced  in  rooms  into 
which  the  products  of  combustion  have  escaped  from  fires  of 
charcoal  or  anthracite.     Carbon  protoxide  is  very  much  more 


124 


CARBON  PROTOXIDE.  —  COMBUSTION. 


[§  19T. 


41. 


poisonous  than  carbonic  acid.  Much  of  the  ill  repute  which 
attaches  to  carbonic  acid  really  belongs  to  carbon  protoxide,  for 
since  both  these  gases  are  produced  by  burning  charcoal,  many 
persons  are  liable  to  confound  them  ;  but  carbonic  acid  is,  com- 
paratively speaking,  almost  innocuous. 

197.  Carbon  protoxide  plays  a  very  important  part  in  many 
metallurgical  operations  on  account  of  the  power  which  it  pos- 
sesses at  high  temperatures  of  taking  away  oxygen  from  many 
compounds  containing  that  element.      Much  of   the  reducing 
action  which  is,  commonly  speaking,  attributed  directly  to  car- 
bon, is  really  effected  in  practice  through  the  mediation  of  the 
protoxide. 

198.  Carbon  protoxide  burns  readily  in  the  air,  the  sole 

product  of  the  burning  be- 
ing carbonic  acid.  The 
gas  forms  an  explosive 
mixture  with  air  or  oxy- 
gen. 

Exp.  82.  —  To    the     ap- 
paratus   employed  in    Exp. 
81,  provided  air  has  not  been 
allowed  to   enter  by  the  cooling  down  of  the 
mixture,  attach   a   piece  of  glass  tubing  drawn 
out  at  the  end  (but  not  to  a  very  fine  point) 
and  bent   in  such   a  manner    that   a  stream  of 
gas  may  be  delivered  upwards  from  the  point. 
Light  the  gas  as  it  flows  out  of  the  tube,  and 
hold  over  the  pale-blue  flame  a  clean,  dry  bottle. 
No  moisture  is  deposited.     That    carbonic  acid 
has  been  produced  may  be  proved  by   pouring 
a  little  lime-water  into  the  bottle  and  shaking 
it  about  in  the  gas  therein  contained. 

199.  Combustion.  —  Now  that  we  have  become  acquainted 
with  carbon,  hydrogen  and  oxygen,  and  with  some  of  the  more 
important  compounds  formed  by  the  union  of  these  elements, 
the  subject  of  combustion  can    be  more  fully  discussed    than 
has  been  possible  hitherto.       The  materials  employed  as  com- 


§201.]          COMBUSTION.  — CHARACTER  OF  FLAMES.          125 

bustibles  are,  as  a  general  rule,  compounds  of  carbon  and  hy- 
drogen ;  there  are  some  exceptions  to  this  rule,  as  when  the 
metal  magnesium  is  burned  for  light,  or  the  heating  of  a  sul- 
phuretted ore  is  eifected  by  the  combustion  of  its  own  sulphur. 

200.  In  almost  all  cases  artificial  light  results  from  the  in- 
candescence  of  particles   of    solid  matter,   or  of  dense  vapors. 
When  the  heat,  which  is  an  invariable  accompaniment  of  chemi- 
cal combination,  can  play  directly  upon  such  solid  or  semi-solid 
particles  with  force  enough  to  ignite  them,  an  exhibition  of  light 
will  accompany  the  chemical  change.     The  hydrogen  flame  af- 
fords no  light,  or  as  good  as  none,  because  in  it  nothing  but  a 
highly  attenuated  gas  is  heated.     But  when  a  solid  body,  such 
as  the  platinum  wire  or  the  piece  of  lime  of  §  41,  is  placed  in 
this  non-luminous  hydrogen  flame,  intense  light  is  radiated  from 
the  heated  solid. 

Exp.  83.  —  Sprinkle  fine  iron  filings  into  the  flame  of  an  alcohol 
lamp,  or  into  the  non-luminous  flame  of  the  gas-lamp,  and  observe  the 
light  given  off  by  the  particles  of  metal  as  they  become  incandescent 
while  passing  through  the  flame.  Or  rub  together  two  pieces  of  char- 
coal above  a  non-luminous  flame,  in  such  manner  that  charcoal  pow- 
der shall  fall  into  the  flame. 

201.  In  ordinary  luminous  flames,  such  as  those  of  candles, 
lamps  and  illuminating  gas,  the  ignited  substance  is  carbon, 
or  rather  a  vapor  or  fog  of  certain  carbon  compounds  contain- 
ing more  or  less  hydrogen. 

Ordinary  illuminating  gas  may  be  decomposed  by  passing  it 
through  a  tube  heated  red-hot :  the  carbon  will  separate,  in  a  finely- 
divided  state,  while  hydrogen  will  escape  from  the  tube  :  or,  by  put- 
ting a  cold  body  into  a  luminous  gas-flame,  the  carbon  is  deposited  as 
soot  (see  Exp.  68,  §  181).  This  breaking  up  of  the  compounds  of 
carbon  and  hydrogen  under  the  influence  of  heat  takes  place  when 
the  gas  is  burned  in  the  air,  and  if  the  supply  of  air  furnished  be 
insufficient  to  convert  all  the  carbon  and  hydrogen  to  carbonic  acid 
and  water,  the  particles  of  carbon  which  escape  unconsumed  will 
cause  the  flame  to  be  smoky.  If  the  supply  of  air  be  excessive,  the 
combustion  will  be  complete,  and  no  light  will  be  afforded  by  the 
flame. 


126  GAS-FLAMES.  —  LAMPS  AND   CANDLES.          [§202. 

If  we  unscrew  the  tube  of  a  common  Bunsen  lamp    (Appendix, 
§  5)  and  light  the  gas  as  it  issues  from  the  slit  (or  holes)  in   the 
lower  part  of  the  burner,  we  shall  have  a  luminous  and  perhaps  even 
smoky  flame.     When,  however,  the  tube  is  in  its  place,  the  gas  be- 
Fig.  42.  comes  mixed  with  air  which  enters  by 

the  holes  at  the  base  of  the  lamp,  and 
when  the  mixture  is  lighted,  the  gas  is 
in  intimate  contact  with  air  enough  to 
burn  it  at  once,  and  completely.  A 
luminous  flame  may  also  be  produced 
by  simply  closing  the  holes  at  the  base 
of  the  lamp,  with  the  fingers  or  by 
means  of  a  metallic  tube,  as  represented 
in  Fig.  42. 

If  across  the  top  of  the  chimney  of  a  lighted  Argand  gas-burner, 
which  is  burning  with  a  low  flame,  we  slip  a  strip  of  sheet-iron,  and 
thus  obstruct  the  flow  of  air,  the  flame  will  increase  in  size,  becoming 
more  and  more  luminous,  and  finally  will  actually  smoke.    The  amount 
Fig.  43.  of  gas  supplied  has  remained  the   same  ;  the 

difference  in  the  amount  of  light  is  owing  to 
the  decrease  of  the  supply  of  air.  The  murky 
flame,  such  as  was  obtained  just  before  actual 
smoking  began,  in  which  the  largest  number  of 
particles  of  carbon  or  heavy  carbonaceous  va- 
por are  heated,  although  none  of  them  are 
heated  very  hot,  yields  the  largest  amount  of 
light  that  can  be  obtained  from  a  given  burner 
with  a  given  sample  of  gas.  Such  a  flame,  how- 
ever, does  not  furnish  the  light  most  agreeable  to  the  eyes. 

202.    The  flames  of  ordinary  lamps  and  candles  are,  strictly 
speaking,  gas-flames. 

Exp.  84.  —  Construct  a  lamp  as  follows  :  To  a  wide-mouthed 
bottle  of  the  capacity  of  about  50  c.  c.  fit  a  cork  loosely  ;  bore  a  hole 
in  the  cork  and  place  therein  a  short  piece  of  glass-tubing,  No.  3, 
open  at  both  ends  ;  through  this  glass-tube  draw  a  piece  of  lamp- 
wicking,  or  any  loose  twine,  long  enough  to  reach  to  the  bottom  of 
the  bottle.  It  is  essential,  either  that  the  cork  should  fit  the  bottle 
loosely,  or  that  there  should  be  a  hole  in  the  cork,  in  order  that  the 


§  202.]  STRUCTURE  OF  FLAMES.  127 

pressure  of  the  external  air  may  act  upon  the  surface  of  the  alcohol, 
—  to  this  end  a  very  small  glass-tube  may  be  inserted  in  the  cork  at 
some  distance  from  the  tube  which  carries  the  wick.  Fill  the  bottle 
nearly  full  of  alcohol,  and,  after  a  few  minutes,  touch  a  lighted 
match  to  the  top  of  the  wick.  The  fluid  alcohol  is  drawn  up  out  of 
the  bottle  by  force  of  capillary  attraction  exercised  by  the  pores  of 
the  vegetable  fibre  of  which  the  wick  is  composed.  When  heat  is 
applied  to  the  alcohol  at  the  top  of  the  wick,  some  of  it  is  converted 
into' vapor  ;  this  vapor  then  takes  fire,  and,  in  burning,  furnishes  heat 
for  the  vaporization  of  new  portions  of  the  alcohol.  From  the  top 
of  the  wick  there  is  constantly  arising  a  column  of  gas  or  vapor,  and 
upon  the  exterior  of  this  conical  column  chemical  combination  is  all 
the  while  going  on  between  its  constituents  and  the  oxygen  of  the 
air.  The  dark  central  portion  of  the  alcohol  flame  is  nothing  but  gas 
or  vapor. 

Exp.  85.  —  Thrust  the  phosphorus  end  of  an  ordinary  friction- 
match  directly  into  the  middle  of  the  flame  of  the  alcohol-lamp  of 
Exp.  84.  The  combustible  matter  upon  the  end  of  the  match  will 
not  take  fire  in  the  atmosphere  of  carbonaceous  gases,  of  which  the 
centre  of  the  flame  consists  ;  the  wood  of  the  match-stick,  of  course, 
takes  fire  at  the  point  where  it  is  in  contact  with  the  outer  edge  of 
the  flame.  The  portion  of  the  match  in  the  centre  of  the  flame 
becomes  so  strongly  heated  during  its  sojourn  within  the  circle  of  fire, 
that  it  is  ready  to  inflame  as  soon  as  it  comes  in  contact  with  the  air  ; 
it  is  therefore  somewhat  difficult  to  withdraw  the  match  from  the 
flame  without  its  taking  fire. 

Exp.  86.  —  Hold  a  thin  wire  (best  of  platinum,  though  iron 
will  answer  well  enough)  or  a  splinter  of  wood  across  the  flame  of 
the  alcohol-lamp,  as  shown  in  Fig.  44.  The  wire  will  Fi«-  44» 
be  heated  to  redness,  and  the  wood  will  burn,  onjy  at 
the  outer  edges  of  the  flame  where  the  gas  and  air 
meet ;  in  the  interior  of  the  flame,  the  wire  will  remain 
dark  and  the  wood  unburned,  for  there  is  no  combus- 
tion there,  and  comparatively  little  heat.  If  the  wire 
be  successively  placed  at  different  heights  in  the  flame 
the  size  and  shape  of  the  internal  cone  of  gas  can  easily  be  made  out ; 
it  will  appear,  moreover,  that  the  hottest  part  of  the  flame  is  just 
above  the  top  of  the  interior  cone  of  gas.  As  a  rule,  when  glass- 
tubing,  or  the  like,  is  to  be  heated  in  a  flame,  it  should  never  be 
placed  below  this  point  of  the  greatest  heat. 


J28  STRUCTURE  OF  FLAMES.  [§  203. 

When  a  candle  is  lighted  for  the  first  time,  the  cotton  of  which  the 
wick  is  composed  takes  fire,  and  is  at  once  consumed  for  the  most 
part,  but,  in  burning,  the  cotton  gives  off  considerable  heat,  and  some 
of  the  wax  or  tallow  of  which  the  candle  is  composed  is  thereby 
melted  and  converted  into  oil.  The  liquid  oil  ascends  the  wick  by 
virtue  of  capillary  attraction,  and  is  converted  into  vapor  or  gas  by 
the  heat  of  the  cotton  still  burning  at  the  stump  of  the  wick  ;  this 
gas  then  burns  precisely  like  the  alcohol  vapor  in-Exp.  84,  and  by 
the  heat  thus  disengaged  new  portions  of  wax  or  tallow  are  continu- 
ally melted.  There  is  always  a  little  cup  of  oil  at  the  top  of  the  rod 
of  wax  or  tallow  of  which  the  candle  consists,  and  the  apparatus  is  as 
truly  an  oil-lamp  as  if  the  oil  were  held  in  a  vessel  of  glass  or  metal. 
If  the  flame  of  the  candle,  when  the  snuff  has  become  long,  be 
blown  out,  a  current  of  vapor  continues  to  ascend  from  the  hot  wick 
and  this  vapor  may  be  ignited  some  distance  above  the  wick.  After 
the  flame  has  been  extinguished,  the  wick  retains  heat  enough  for  a 
few  moments  to  distil  off  a  quantity  of  gas,  although  there  is  not 
heat  enough  generated  to  inflame  this  gas.  To  the  gas  or  vapor  thus 
evolved  is  to  be  referred  the  disagreeable  odor  which  is  observed 
when  a  candle  is  blown  out. 

Exp.    87. —  Press   down  a  piece   of    white    letter-paper,   for  an 
instant,  upon  the  flame  of  a  candle  until  it  almost  touches  the  wick, 
then  quickly  remove  the  paper  before  it  takes  fire,  and  observe  that 
Fig.  45.  its  upper  surface  is  charred  in  the  manner 

shown  in  Fig.  45.  There  will  be  obtained, 
in  fact,  burned  into  the  paper,  a  diagram 
of  the  part  of  the  flame  where  combustion 
is  taking  place.  It  is  thus  seen  to  be  ring- 
shaped  in  section,  and  to  enclose  a  space  where  no  combustion  is 
going  on. 

203.  All  flames,  which  are  rendered  luminous  by  incandes- 
cent carbonaceous  particles,  have  the  same  general  structure. 
This  structure  is  best  studied  in  the  flame  of  a  candle. 

In  the  candle-flame  four  portions  or  divisions  of  the  flame  can  be 
distinguished  (Fig.  46).  First,  there  is  the  small  blue  cup- shaped 
portion  of  the  flame  (a  V)  at  the  base  of  the  wick  ;  here  a  part  of  the 
combustible  gases  coming  from  the  wick  are  burned  completely,  as  the 
oxygen  of  the  air  has  free  access  tp  this  part  of  the  flame.  The  heat 
thus  produced  converts  into  vapor  the  oil  which  the  wick  draws  up 


§  204.]  PRINCIPLE  OF  THE  BLOWPIPE.  129 

from  the  candle.     This  carbonaceous  vapor  rises  and  forms  the  second 
part  of  the  flame,  the  non-luminous  cone  (c).     Here  no  combustion 
can  take  place  :  the  oxygen  of  the  air,  it  is  true,  tends  to  pass,  by  dif- 
fusion, into  the  interior  of  the  flame  ;  but,  as  fast  as  it     Fig.  46. 
approaches,  it  meets  carbon  and  hydrogen  in  the  outer 
portion  of  the  flame,  and  enters  into  combination  with 
these  elements  :   the  nitrogen  of  the  air,  however,  dif- 
fuses freely  into  the  interior  of  the  flame,  and  is  found, 
mixed  with  the  combustible   gases  of  the   candle   and 
with  some  carbonic  acid  and  steam,  in  the  space  (c). 

The  third  portion  of  the  flame  is  the  luminous  zone  (d). 
Here  the  combustion  is  incomplete  ;  the  gaseous  com-; 
pounds  of  carbon  and  hydrogen  are  broken  up  by  heat 
into  their  constituent  elements.  The  carbonaceous  par- 
ticles are  intensely  ignited,  and  burn  to  carbon  pro- 
toxide by  taking  oxygen  from  the  air,  and  also  from  the 
carbonic  acid  and  steam  which  diffuse  inwards  from  the 
outermost  portion  of  the  flame. 

The  fourth  portion  of  the  flame  is  the  thin,  scarcely  perceptible, 
non-luminous  mantle  (fef)  which  surrounds  the  entire  flame.  Here 
the  carbon  protoxide  and  hydrogen  burn  to  carbonic  acid  and  steam, 
and,  as  has  already  been  seen,  a  part  of  these  gases  diffuse  inwards 
and  are  decomposed,  furnishing  oxygen  for  the  partial  combustion  of 
the  carbon  in  the  luminous  portion  of  the  flame. 

204.  The  principle  of  the  oxy-hydrogen  blowpipe,  as  well 
as  of  the  ordinary  blast  lamps  in  which  air  and  illuminating  gas 
are  used  instead  of  oxygen  and  hydrogen,  is  the  throwing  of 
oxygen  into  the  combustible  gas  so  that  the  combustion  is  in- 
tense and  concentrated.  On  the  same  principle  depends  the  use 
of  the  mouth-blowpipe. 

(For  a  description  of  the  mouth-blowpipe,  see  Appendix,  §  7.) 
Exp.  88. —  To  use  the  mouth-blowpipe,  place  the  open  end  of 
the  tube  between  the  lips,  or,  if  the  pipe  is  provided  with  a  mouth- 
piece, press  the  trumpet-shaped  mouth-piece  against  the  lips ;  fill  the 
mouth  with  air  till  the  cheeks  are  widely  distended,  and  insert  the  tip 
in  the  flame  of  a  candle  or  of  a  lamp  with  a  flat  wick  ;  close  the  com- 
munication between  the  lungs  and  the  mouth,  and  force  a  current  of  air 
through  the  tube  by  squeezing  the  air  in  the  mouth  with  the  muscles 
of  the  cheeks,  breathing,  in  the  mean  time,  regularly  and  quietly 


130 


OXIDIZING  AND  REDUCING  FLAME. 


[§  205. 


through  the  nostrils.     The  knack  of  blowing  a  steady  stream  for  sev- 
eral minutes  at  a  time  is  readily  acquired  by  a  little  practice. 

It  is  possible  with  the  blowpipe  to  produce  either  an  oxidizing 
or  a  reducing  flame,     When   the  jet  of  the  blowpipe  is  inserted 
into  the  lamp  or  gas-flame,  as  shown  in  Fig.  47,  and  a  strong  blast  is 
Fig.  47.  forced  through  the  tube,   a 

blue  cone  of  flame  (a  b)  is 
produced,  beyond1  and  out- 
side of  which  stretches  a 
more  or  less  colored  outer 
cone  (a  c).  The  point  of 
greatest  heat  in  this  flame  is 
at  the  point  of  the  inner 
blue  cone  ;  oxidation  takes 
place  most  rapidly  at,  or  just  beyond  the  point  (c)  of  the  flame,  pro- 
vided that  the  temperature  at  this  point  is  high  enough  for  the  special 
substance  to  be  heated. 

To  obtain  a  good  reducing  flame,  it  is  necessary  to  place  the  tip 
of  the  blowpipe,  not  within,  but  just  outside  of  the  flame,  and  to  blow 
somewhat  gently  over  rather  than  through  the  middle  of  the  flame 
Fig.  48.  (Fig.    48).     In   this  manner, 

7r~\  the   flame  is  less  altered  in 

— "^  its    general     character    than 

in  the  former  case,  the  chief 
part  consisting  of  a  large, 
luminous  cone,  containing  a 
quantity  of  free  carbon  in  a 
state  of  intense  ignition  and 
just  in  the  condition  for  tak- 
ing up  oxygen.  This  flame  is,  therefore,  reducing  in  its  effect.  The 
substance  which  is  to  be  reduced  by  exposure  to  this  flame  should  be 
completely  covered  up  by  the  luminous  cone,  so  that  contact  with 
the  air  may  be  entirely  avoided. 

205.  Instead  of  forcing  the  air  (or  oxygen)  into  the  burning 
fuel,  the  supply  of  air  may  be  furnished  by  means  of  chimneys. 
Chimneys,  whether  of  lamps  or  furnaces,  are  simply  devices  for 
bringing  an  abundance  of  air,  and  therefore  of  oxygen,  into  the 
fire ;  that  in  so  doing  they,  at  the  same  time,  carry  off  the  waste 
products  of  combustion  is  an  incidental  advantage. 


§  205.]  EXPERIMENTS  ON  COMBUSTION.  131 

Exp.  89.  —  Light  a  piece  of  a  candle  8  or  10  c.  m.  long,  and 
stand  it  upon  a  smooth  table  ;  over  the  candle  place  a  rather  tall, 
narrow  lamp-chimney  of  glass,  the  bottom  Fig.  49. 

of  the  chimney  being  made  to  rest  upon 
the  table,  and  observe  that  the  candle- 
flame  will  soon  be  extinguished.  No  fresh 
air  can  enter  the  chimney  from  below  to 
maintain  the  chemical  action,  and  the 
small  quantity  of  air  which  can  creep 
down  the  chimney  from  above  is  alto- 
gether insufficient  to  meet  the  require- 
ments of  the  case. 

Exp.  90.  —  Relight  the  candle  of  Exp. 
89,  and  again  place  over  it  the  lamp-chimney  ;  but  instead  of  allow- 
ing the  chimney  to  rest  closely  upon  the  surface  of  the  table,  prop  it 
up  on  two  narrow  strips  of  wood,  so  the  air  can  have  free  en- 
trance into  the  chimney  from  below.  The  candle  will  now  continue 
to  burn  freely,  for  the  heavy,  cold  air  outside  will  continually  press 
into  the  lower  part  of  the  chimney,  and  push  out  the  warm,  light 
products  of  combustion,  and  the  candle-flame  will  all  the  while  be 
supplied  with  fresh  air. 

The  direction  of  the  current  of  air  may  be  shown  by  placing  a 
piece  of  burning  "touch-paper"  at  the  foot  of  the  chimney.  Touch- 
paper  is  made  by  soaking  ordinary  brown  paper  in  a  strong  solution 
of  potassium  nitrate,  and  then  drying  it.  On  being  lighted,  the  paper 
burns  without  flame,  while  emitting  clouds  of  smoke. 

Exp.  91.  —  Repeat  Exp.  90,  and  when  the  candle  is  burning 
quietly,  cover  the  top  of  the  chimney  tightly  with  a  piece  of  tin  or 
sheet-iron,  or  with  a  strip  of  window-glass  ;  the  candle  will  soon 
cease  to  burn  precisely  as  if  the  chimney  were  closed  at  the  bottom, 
for,  the  escape  of  the  hot  products  of  combustion  being  prevented, 
no  air  can  pass  into  the  chimney  to  reach  the  candle-flame. 

It  is  by  inducing  the  current  of  fresh  air  (Exp.  90),  or  draught, 
as  it  is  ordinarily  termed,  that  chimneys  are  specially  useful.  Through 
the  chimney  the  hot  air  from  the  lamp  flows  straight  forward  and 
rapidly,  and,  of  course,  a  correspondingly  direct  and  rapid  current 
of  fresh  air  presses  in  to  supply  its  place.  Owing  to  this  power  of 
rapidly  supplying  air,  chimneys  are  employed  upon  lamps  burning 
petroleum  and  other  highly  carbonized  oils  which  are  liable  to  smoke. 

Exp.  92.  —  It    is    not  absolutely  necessary  that  the    fresh    air 


132  KINDLING-TEMPERATURE.  [§  206. 

should  flow  into  a  chimney  from  below.     Divide  the  upper  part  of 
Fig.  5O.  the  chimney  of  Exp.  89  into  two  channels, 

by  hanging  in  it  a  strip  of  sheet-iron  or  tin, 
as  a  partition  at  the  centre  of  the  chimney 
(see  Fig.  50).  Place  the  chimney  thus 
divided  over  a  burning  candle,  and  observe 
that  the  candle  will  continue  to  burn  as  if 
in  a  strong  draught  of  air,  although  no  air 
can  enter  the  chimney  from  below.  Hold  a 
piece  of  burning  touch-paper  at  the  top  of 
the  divided  chimney  ;  the  smoke  will  be 
drawn  down  into  the  chimney  on  one  side 
of  the  partition,  and  thrown  out  again  upon 
the  other,  as  indicated  by  the  arrows  in  Fig.  50.  It  appears  from 
this,  as  well  as*  from  the  tremulous  motion  of  the  flame,  that  a  current 
of  cold  air  presses  down  upon  one  side  of  the  division  wall  and  sup- 
plies the  required  oxygen. 

206.  Kindling-Temperature,  —  In  order  that  any  combusti- 
ble substance  shall  burn,  or,  in  other  words,  in  order  that  brisk 
chemical  action  shall  occur  between  the  combustible  and  the 
oxygen  of  the  air,  it  must  first  be  heated  to  a  certain  tempera- 
ture, and  then  kept  at  that  heat.  The  temperature  at  which 
any  substance  takes  fire  is  known  as  the  kindling-temperature 
of  that  substance. 

Exp.  93.  —  Place  a  small  bit  of  phosphorus  and  another  of  sul- 
phur, not  in  contact  with  the  first,  upon  a  fragment  of  porcelain  6  or 
8  c.  m.  across,  and  heat  them  slowly  over  the  gas-lamp  ;  the  phos- 
phorus will  soon  take  fire  at  a  temperature  of  68°-70°,  but  the  sulphur 
will  not  inflame  until  the  temperature  of  the  porcelain  support  has 
risen  to  about  250°,  as  can  be  ascertained  by  the  thermometer. 

As  was  just  now  said,  the  degree  of  heat  necessary  to  start  any 
fire  must  be  kept  up  continually,  or  the  fire  will  go  out.  When- 
ever burning  bodies  are  cooled  below  the  kindling-temperature, 
they  are  extinguished,  —  the  chemical  action  which  occasioned 
the  appearance  of  heat  and  light  ceases. 

If  we  pile  up  upon  a,n  iron  grate,  thick  in  metal,  and  supported  in 
such  manner  that  air  may  enter  beneath  it,  several  pieces  of  red-hot 


§  207.]  KIXDLING-TEMPERATURE.  133 

charcoal,  the  charcoal  will  go  on  burning  until  nearly  all  of  it  has 
been  consumed,  for  the  heat  generated  by  the  combustion  of  the  por- 
tions first  burned  keeps  up  the  temperature  necessary  to  kindle  the 
subsequent  portions.  If,  however,  we  scatter  about  upon  a  cold  grate 
several  small  pieces  of  red-hot  charcoal,  taking  care  that  no  two 
pieces  of  the  coal  shall  come  in  contact,  or  -be  placed  so  as  to  heat  one 
another,  each  of  the  pieces  of  charcoal  will  soon  cease  to  burn  ;  for 
the  metallic  grate  is  so  good  a  conductor  of  heat  that  it  removes  heat 
from  the  isolated  pieces  of  charcoal  more  rapidly  than  these  can  pro- 
duce it  :  the  temperature  of  the  charcoal  is,  consequently,  soon  re- 
duced to  below  the  kindling-point. 

207.  Precisely  as  coals  can  be  extinguished  by  placing  them 
upon  cold  metal,  so  flames  may  be  put  out. 

Exp.  94.  —  Upon  a  ring  of  the  iron-stand  place  a  sheet  of  clean 
wire-gauze  about  10  c.  m.  square  ;  lower  the  ring  so  that  the  gauze 
shall  be  pressed  down  upon  the  flame  of  a  lamp  or  candle  almost  to 
the  wick,  as  shown  in  Fig.  51.  No  flame  will  be  seen  above  the 
gauze,  but  instead  of  flame  a  cloud  of  smoke.  Fis»  51. 

The  gauze  is  a  mere  open  sieve  ;  there  is  nothing 
about  it  which  can  prevent  the  gas,  which  was  ?/>'  ^ 

just  now  burning  with  flame  above  the  wick  of 
the  candle,  from  passing  through.  Indeed,  it 
may  be  seen  from  the  smoke  that  the  particles 
of  carbon  which,  in  the  original  undisturbed 
flame,  were  becoming  incandescent,  and  so  affording  light,  do  now 
actually  come  through  the  gauze. 

The  explanation  of  the  phenomenon  is  simply  that  the  metallic 
sieve  conducts  away  so  much  heat  that  the  temperature  of  the  candle- 
flame  is  reduced  to  below  the  kindling-point.  That  this  is  really  so, 
is  proved  by  the  fact,  that  after  the  gauze  has  become  sufficiently 
heated  by  long-continued  contact  with  the  flame  below,  —  after  it  has 
attained  the  kindling-point  of  the  candle-gas,  —  it  will  no  longer 
extinguish  the  flame.  In  like  manner,  a  candle-flame  may  be  cooled 
to  such  an  extent  that  it  will  go  out  by  placing  over  it  a  small  coil  of 
cold  copper  wire,  while,  if  the  wire  be  previously  heated,  the  flame 
will  continue  to  burn. 

If  the  smoke  and  unburned  gas  which  has  passed  through  the  cold 
wire-gauze  be  touched  with  a  lighted  match,  and  so  brought  to  the 
kindling-temperature,  it  will  burst  into  flame, 
12 


134  SAFETY-LAMPS.  [^  207. 

The  power  of  wire-gauze  to  prevent  the  passage  of  flame  has  been 
usefully  applied  in  several  ways,  notably  for  the  prevention  of  explo- 
sions in  those  coal-mines  which  are  liable  to  accumulations  of  marsh- 
gas  (§  215).  For  this  purpose  safety-lamps  are  constructed  by  enclos- 
ing an  ordinary  oil-lamp  completely  in  wire-gauze,  so  that  the  flame 
within  the  gauze  can  not  kindle  any  combustible  or  explosive  gas 
into  which  it  may  be  carried.  In  case  such  a  lamp  be  carried  into  a 
place  filled  with  explosive  gas,  the  latter  will,  of  course,  pass  into 
the  lamp  through  the  meshes  of  the  gauze,  and  burn  within  the  cage. 
This  combustion  gives  warning  of  the  presence  of  the  dangerous 
gas,  and  indicates  to  the  workman  that  he  should  withdraw  from  the 
locality  :  the  gas  can  then  be  expelled  by  appropriate  methods  of 
ventilation. 

Exp.  95.  —  Beneath  a  sheet  of  wire-gauze  resting  on  a  ring  of  the 
lamp-stand,  place  an  unlighted  Bunsen's  burner,  at  such  a  distance 
52.  that  the  gauze  shall  be  3  or  4  c.  m.  above  the  top  of 
the  lamp  ;  turn  on  the  gas  and  light  it  above  the  wire- 
gauze  :  it  will  continue  to  burn  on  top  of  the  gauze  for 
an  indefinite  period,  for  the  gauze  will,  in  this  case, 
always  be  kept  cool  by  the  cold  gas  which  is  continu- 
ally passing  through  it.  Carefully  and  gradually  lift 
the  ring  which  carries  the  gauze,  and  determine  how 
far  it  is  possible  to  lift  the  gauze  above  the  gas-jet  with- 
out extinguishing  the  flame. 

An  effect  somewhat  similar  to  that  produced  by  wire-gauze  is  often 
seen  in  ordinary  fires.  When  a  mass  of  red-hot  anthracite,  charcoal 
or  coke  is  burning  freely  upon  a  grate  in  the  open  air,  there  is  always 
a  blue  flame  of  carbon  protoxide  burning  above  the  coal.  This  gas 
results  from  the  reduction  of  carbonic  acid  by  means  of  hot  carbon. 
Air  enters  at  the  bottom  of  the  grate  and  combines  with  the  hot  coal 
which  it  finds  there  to  form  carbonic  acid,  CO2.  This  carbonic  acid, 
as  it  rises  through  the  hot  coal  in  the  middle  of  the  fire,  is  deprived 
by  the  heated  carbon  of  half  its  oxygen  :  CO2  -|-  C  =  2  CO.  The 
carbon  protoxide  being  combustible,  will  at  once  take  fire  on  coming 
in  contact  with  the  air,  provided  the  temperature  at  the  summit 
of  the  fire  be  equal  to  the  kindling-temperature  of  this  gas.  But  if 
the  temperature  of  the  fire  is  in  any  way  reduced  below  this  point,  as, 
for  example,  by  throwing  on  too  large  a  quantity  of  cold  fuel,  which 
is,  of  course,  equivalent  to  covering  the  fire  with  a  sheet  of  wire- 
gauze,  then  the  carbon  protoxide  will  be  extinguished,  and,  escaping 
into  the  chimney,  will  produce  no  useful  effect. 


§  209.]  CARBON  BISULPHIDE.  135 

208.  Carbon  and  Sulphur.  —  Carbon  bisulphide  (CS2)  is 
interesting  from  its  correspondence  to  carbonic  anhydride,  CO.,, 

and  forms  another  instance  of  the  analogy  between  the  com- 
pounds of  oxygen  and  sulphur.  Carbon  bisulphide  is  prepared 
by  passing  the  vapor  of  sulphur  over  red-hot  charcoal.  It  is  a 
colorless,  strongly-refracting  liquid  which  boils  at  about  54°  and 
evaporates  rapidly  at  the  ordinary  temperature  of  the  air.  It 
possesses  an  ethereal  odor  when  purified,  but  the  common  bisul- 
phide has  a  peculiar  and  very  disagreeable  smell.  It  is  very 
inflammable  and  burns  with  a  blue  flame,  the  product  of  the 
combustion  being  carbonic  and  sulphurous  anhydrides.  It  is 
used  as  a  solvent  of  phosphorus  and  sulphur,  and  is  employed  in 
the  cold  process  of  vulcanizing  caoutchouc. 

Exp.  96.  —  Into  a  small  beaker  or  watch-glass  put  two  teaspoon- 
fuls  of  carbon  bisulphide.  Set  the  glass  upon  a  wet  piece  of  wood, 
and  by  means  of  a  glass  tube  direct  a  current  of  air  from  the  lungs, 
or  from  a  pair  of  bellows,  across  the  surface  of  the  liquid.  The 
volatile  carbon  bisulphide  rapidly  evaporates,  and  in  so  doing  pro- 
duces such  an  amount  of  cold,  that  the  glass  will  be  frozen  to  the 
wood.  This  experiment  should  be  performed  where  there  is  a  good 
draught  of  air,  and  out  of  the  neighborhood  of  any  lighted  lamp. 


CHAPTER  XV. 

CARBON  (continued). 

209.  Carbon  unites  with  hydrogen,  oxygen  or  nitrogen,  or 
with  two  of  these  elements,  or  with  all  three  of  them,  in  the 
most  varied  proportions.  A  great  number  of  different  com- 
pounds are  thus  formed,  some  of  them  being  extremely  com- 
plex. Since  many  of  these  more  complex  compounds  of  carbon 
occur  ready  formed  in  animals  and  plants,  or  are  produced  by 
the  transformation  of  substances  derived  from  these  sources, 
they  are  usually  classed  together  and  studied  under  the  head  of 
"Organic  Chemistry." 


136  CYANOGEN.  —  CYANHYDRIC  ACID.  [§  210. 

There  is  no  sufficient  reason,  chemically  speaking,  for  making  this 
division  :  chemical  compounds,  whether  derived  from  the  animal, 
vegetable  or  mineral  kingdoms,  are  governed  by  the  same  laws  :  it  is, 
moreover,  impossible  to  draw  any  sharp  line  of  demarcation  between 
organic  and  inorganic  chemistry  ;  still,  on  account  of  the  vast  number 
of  the  carbon  compounds,  the  mere  names  of  which  would  fill  a 
volume,  this  arrangement  has  the  merit  of  convenience.  In  this  and 
the  two  following  chapters  a  few  of  the  more  important  of  these  so- 
called  organic  bodies  will  be  considered. 

Other  elements  besides  those  already  mentioned,  such  as  sulphur 
and  phosphorus,  enter  into  the  composition  of  these  bodies.  Many 
of  the  complex  substances  which  exist  in  the  bodies  of  animals,  such 
as  albumin  and  the  matter  which  forms  the  substance  of  the  hair, 
contain  sulphur  as  an  essential  ingredient.  Moreover,  the  numerous 
organic  acids  form  salts  of  the  various  metals,  and  many  of  these  salts 
exist  ready  formed  in  nature. 

210.  Carbon  and  Nitrogen.— Prominent  among  the  compounds 
of  carbon  and  nitrogen  is  cyanogen  (CN),  which  is  an  important 
compound  radical,  and  which  also  exists  in  the  free  state. 

211.  Cyanogen  (CN  or  Cy). — Carbon  and  nitrogen  do  not 
unite  directly,  but  when  a  current  of  nitrogen  is  passed  over 
red-hot  charcoal  which  has  been  previously  soaked  in  a  solution 
of  potassium  carbonate,  there  is  formed  potassium  cyanide,  a 
compound  containing  the  radical  cyanogen. 

K2C03  -r4C  +  2N  =  2  KCN  +  3  CO. 

Free  Cyanogen  is  best  prepared  by  heating  mercuric  cyanide ; 
thus, — HgCy3  =:  Hg  +  2  Cy.  It  is  a  colorless,  poisonous  gas  of 
suffocating  odor  and  ready  inflammability.  Its  molecule  contains 
two  atoms  of  the  radical  and  is  written  (CN)2. 

212.  Cyanhydric  Acid  (HCN).  —  Cyanhydric  acid,  which  may 
be  prepared  by  passing  hydrogen  sulphide  over  mercury  cyan- 
ide  (Hg  (CN)2  -f-  H2S  —  HgS  -{-  2  HCN),  is  a  combustible  and 
volatile  liquid  :  it  possesses  the  odor  of  bitter  almonds  and  is 
intensely  poisonous.    In  aqueous  solution  it  is  known  as  prussic 
acid. 

Several  of  the  cyanides  are  important  bodies,  and  will  be 
mentioned  under  the  head  of  the  different  metallic  elements. 


§214.]         HYDROCARBONS.— METHYL  HYDRIDE.  137 

They  correspond  in  composition  to  the  chlorides,  the  univalent 
radical  (§  154)  ON  occupying  the  place  of  Cl ;  thus  potassium 
cyanide  is  KCN ;  zinc  cyanide  is  Zn(CN)2. 

Exp.  97.  —  To  a  very  minute  quantity  of  solid  potassium  cyanide, 
add  a  few  drops  of  strong  sulphuric  acid.  The  effervescence  which 
takes  place  is  due  to  the  escape  of  cyanhydric  acid,  which  may  be 
recognized  by  its  peculiar  odor.  The  reaction  is  similar  to  that 
which  takes  place  when  common  salt  is  treated  with  sulphuric  acid  in 
the  production  of  chlorhydric  acid.  It  may  be  expressed  as  follows  : 
2  KCN  -f  H2S04  =  K2S04  -f  2  HCN. 

The  cyanates  correspond  to  cyanic  acid  (HCyO).  Thus,  potas- 
sium cyanate  is  KCyO. 

213.  Compounds  of  Carbon  and  Hydrogen  or  Hydrocarbons 

are  very  numerous.  We  first  consider  one  of  the  most  familiar 
of  them,  marsh-gas. 

214.  Methyl  Hydride  or  Marsh-Gas  (CH4).  —  In  hot  sum- 
mer weather  bubbles  of  gas  are  often  seen  rising  to  the  sur- 
face of  stagnant  pools  :  if  a  pole  be  thrust  into  the  mud  at 
the  bottom  of  the  pool,  a  considerable  amount  of  the  gas  will 
rise  and  may  be  collected  by  holding  an  inverted  bottle  full  of 
water   over   the   ascending   bubbles.      The   gas   thus   collected 
contains  a  certain   amount   of   carbonic   acid    (which  may   be 
removed  by  putting  some  milk  of  lime  into  the  bottle,  and 
shaking  it  for  a  short  time),  together  with  a  little  nitrogen  : 
the  greater  part,  however,  consists  of  a  colorless  gaseous  com- 
pound of  carbon  and  hydrogen.     This  gas  is  a  product  of  the 
putrefaction   of   vegetable  matter  under  water,  where  the  sup- 
ply of  air  is  insufficient  to  oxidize  the  whole  of  the  organic 
matter  to  carbonic  acid  and   water  ;  hence  the  name  marsh- 
gas. 

The  formula  of  marsh-gas  is  CH4,  and  it  may  be  regarded  as  a 
compound  of  hydrogen  (H)  with  a  group  of  atoms  (CH3)  called 
methyl.  This  group  of  atoms  (CH3)  like  the  group  (NH4)  which 
has  been  designated  as  ammonium  (§  67),  and  like  cyanogen 
(§211),  takes  part  in  chemical  transformations  as  if  it  were  a  simple 
elementary  atom.  The  chemical  name  of  marsh-gas  is  methyl 
hydride,  or  methane. 
12* 


138  METHYL  HYDRIDE  OR   MARSH-GAS.  [§  215. 

215.  Methyl  hydride  forms  a  very  considerable  portion  of 
ordinary  illuminating  gas  made  by  distilling  coal ;  from  some 
varieties   of  bituminous   coal,  it  is  disengaged  at  the  ordinary 
temperature,  and  forms  the   "  fire-damp "  of   coal-mines ;    like 
hydrogen,  it  forms  an  explosive  mixture  with  air,  and  the  ex- 
plosion of  this  mixture  in  badly-ventilated  mines  is  often  the 
cause  of  frightful  loss  of  life.     The  gas  may  be  prepared  arti- 
ficially as  follows  :  — 

Exp.  98.  —  Mix  together  two  grms.  of  crystallized  sodium  acetate, 
4  grins,  of  caustic  soda  and  8  grins,  of  slaked  lime.  Heat  the  mix- 
ture gently  upon  an  iron  plate,  until  all  the  water  of  crystallization 
of  the  acetate  has  been  expelled,  and  the  mass  has  become  dry  and 
friable.  Charge  an  "ignition-tube  20  c.  in.  long  with  the  dry  powder, 
Fig.  53.  heat  it  above  the  gas-lamp,  and 

collect  the  gas  at  the  water-pan. 
Marsh-gas  is  evolved  from  the  mix- 
ture, at  a  temperature  below  red- 
ness, and  a  residue  of  sodium  car- 
bonate is  left  in  the  ignition-tube. 
The  purpose  of  the  lime  is  to  ren- 
der the  mass  porous  and  infusible, 
or  nearly  infusible,  so  that  the  tube 
may  be  heated  equably.  The  re- 
action may  be  represented  as  follows  :  — 

NaC2H302  -f  NaHO  =  CH4  -f  Na2CO3. 

Dry  sodium  Sodium  Marsh-  Sodium 

acetate.  hydrate.  gas.  carbonate. 

216.  Marsh-gas  is  transparent,  colorless  and  little  more  than 
half  as  heavy  as  air.     Next  to  hydrogen  it  is  the  lightest  known 
substance,  its  specific  gravity  being  only  8.     It  takes  fire  readily 
when  touched  with  a  lighted  match,  and  burns  with  a  bluish- 
yellow  flame. 

217.  That  marsh-gas  really  contains   hydrogen   and   carbon 
may  be  readily  proved  by  bringing  into  play,  under  appropriate 
conditions,  the  strong  affinity  of  chlorine  for  hydrogen. 

Exp.  99.  —  Fill  a  tall  bottle  of  at  least  one  litre  capacity  with 
warm  water,  invert  it  over  the  water-pan,  and  pass  marsh-gas  into 
it,  until  a  little  more  than  one-third  of  the  water  is  displaced  ;  cover 


§  219.]  CHLOROFORM.  -ILLUMINATING  GAS.  139 

the  bottle  with  a  thick  towel,  to  exclude  the  light,  and  then  fill  the 
rest  of  the  bottle  with  chlorine.  Cork  the  bottle  tightly,  and  shake 
it  vigorously,  in  order  to  mix  the  gases  together,  keeping  the  bottle 
always  covered  with  the  towel.  Finally,  open  the  bottle  and  apply  a 
light  to  the  mixture.  Ignition  takes  place,  chlorhydric  acid  is  pro- 
duced, while  the  sides  and  mouth  of  the  bottle  become  coated  with 
solid  carbon  in  the  form  of  lamp-black.  The  presence  of  the  acid 
may  be  proved  by  the  smell,  by  its  reaction  with  moistened  blue 
litmus-paper,  and  by  the  white  fumes  which  are  generated  when  a 
rod  moistened  with  ammonia-water  is  brought  in  contact  with  the 
escaping  acid  gas. 

218.  Chloroform  (CHC13).  —  When   chlorine  is  allowed  to   act 
slowly  on  marsh-gas,  there  is  formed,  besides  carbon  quadrichloride 
(CC14),  a  compound  having  the  formula  CHC13  and  called   chloro- 
form.    Chloroform  (CHC13)  may  be  regarded  as  marsh-gas,  in  which 
three   atoms   of  hydrogen   have   been    replaced  by  three   atoms   of 
chlorine.     It  is  manufactured  in  practice  by  distilling  dilute  alcohol 
with  "  chloride  of  lime."      Water  and  chloroform  come  off  together, 
but  do  not  mix  in  the  receiver  :  the  chloroform,  being  the  heavier, 
sinks  to  the  bottom,  and  may  be  withdrawn  and  purified.     Chloro- 
form is  a  colorless,  volatile  liquid,  the  vapor  of  which  when  inhaled 
causes  temporary  insensibility  to  pain,  and  on  this  account  it  is  used 
in  surgical  operations. 

219.  Illuminating   Gas. —  The   principle    involved   in   the 
manufacture  of  illuminating  gas  has   already   been   illustrated 
in  Exps.  65  and  66.     Illuminating  gas  is  ordinarily  prepared  by 
distilling  bituminous  coal ;  other  substances  made  up  wholly  or 
in  part  of  compounds  of  hydrogen  and  carbon,  such  as  wood, 
oil,  resin,  petroleum  and  even  bones,  are  sometimes  used.     Fig. 
54  shows  in  a  general  way  the  processes  involved  in  the  manu- 
facture and  purification  of  coal-gas. 

The  coal  is  introduced  into  the  retorts,  C,  which  are  cylindrical  01 
semi-cylindrical  tubes  of  clay  or  iron,  arranged  in  sets  of  three  or 
five,  or  even  more,  and  heated  by  a  coke  fire  burning  on  the  grate- 
bars,  A.  All  the  products  of  the  distillation,  except  the  coke  which 
remains  in  the  retort,  are  volatile  at  the  high  temperature  employed, 
and  pass  up  the  vertical .  pipe.  T.  The  relative  proportions  of  these 
products,  and  to  a  certain  extent  their  character,  depend  on  the 
quality  of  coal  employed,  and  on  the  temperature  at  which  the  dis- 


140 


MANUFACTURE  OF  COAL-GAS. 


[§  219. 


§  220.]  ILLUMINATING  GAS.  HI 

tillation  takes  place  :  it  may,  however,  be  said  in  general  terms  that 
these  products,  when  cooled  to  the  ordinary  temperature,  are  of  three 
kinds,  —  solid,  liquid  and  gaseous. 

The  gases  obtained  by  the  distillation  of  coal  are  marsh-gas, 
defiant-gas  (§  259),  carbon  protoxide,  carbonic  acid,  hydrogen,  nitro- 
gen, aqueous  vapor  and  hydrogen  sulphide  ;  the  liquid  portion  of  the 
distillate  consists  of  an  aqueous  solution  of  ammonium  carbonate, 
sulphide  and  sulphocyanide,  certain  liquid  hydrocarbons,  such  as 
benzol,  toluol  etc.,  which  will  be  considered  hereafter  (§  264),  and  a 
semi-liquid  or  viscous  tar.  The  solid  product  of  the  distillation  of 
coal  is  the  coke  left  in  the  retort. 

In  the  production  of  gas,  all  the  volatile  products  of  the  distillation 
go  up  the  pipe,  T,  which  is  curved  at  its  upper  extremity,  and  dips 
into  water  in  the  "  hydraulic  main,"  B.  In  this  water  a  portion  of 
the  tar  and  aqueous  vapor  is  condensed,  and  the  ammoniacal  salts  are, 
in  part,  dissolved.  The  gas  then  passes  alternately  up  and  down 
through  the  cooling  pipes,  D,  called  the  "condensers,"  and  suffers 
further  condensation,  the  remaining  tar  and  the  liquid  hydrocarbons 
being  deposited.  The  gas  is  often  further  purified  by  passing  through 
a  tower,  0,  filled  with  fragments  of  coke,  over  which  water  trickles, 
the  water  absorbing  the  ammoniacal  salts  still  present.  The  gas  then 
passes  through  the  purifier,  M,  where  it  comes  in  contact  with  slaked 
lime  and  is  freed  from  hydrogen  sulphide  and  most  of  its  carbonic 
acid,  and  thence  into  the  gas-holder,  G.  The  lime  in  the  purifiers  is 
sometimes  replaced  wholly  or  in  part  by  dry  ferric  hydrate,  which 
retains  the  hydrogen  sulphide. 

220.  After  purification,  the  gas  as  delivered  to  the  consumer 
consists  mainly  of  marsh-gas,  hydrogen  and  carbon  protoxide, 
• —  t&e  marsh-gas  usually  amounting  to  about  one-third  part 
of  the  whole  gas.  These  non-luminous,  or  very  feebly  lumi- 
nous gases,  serve  as  carriers  of  the  six  or  seven  per  cent  of  real 
light-producing  ingredients  which  are  contained  in  the  gas. 
This  mixture  of  light-giving  ingredients  is  exceedingly  complex. 
The  vapor  of  benzol,  no  doubt,  plays  a  prominent  part ;  some 
of  the  higher  members  of  the  marsh-gas  series  lend  their  aid, 
and  a  hydrocarbon  of  composition  C2H2,  called  acetylene,  is 
important  and  very  generally  present.  Sometimes  a  little  olefi- 
ant  gas  (C2H4)  is  present,  but  the  old  view,  that  this  substance 
constitutes  the  chief  luminiferous  ingredient  of  coal-gas,  is  no 
longer  admitted. 


142  MARSH-GAS.  — PETROLEUM.  [§  221. 

The  coal-tar  obtained  as  a  waste  product  in  the  gas  manufacture  is 
a  very  complex  substance.  Among  other  substances  it  contains 
benzol,  used  in  the  manufacture  of  aniline  colors,  and  aniline  itself 
in  very  small  proportion  ;  from  it  is  obtained  the  pitch  used  as  a  roof- 
ing material  and  for  sidewalks. 

221.  Marsh-gas    is    the  first    of  a   series    of   hydrocarbons, 
each  member  of  which   differs  in  formula  from  the  preceding 
one  by  CH2.     This  series  may  be  arranged  in  tabular  form,  as 
follows  :  — 

Marsh-gas  Series. 

Name.  Formula.  Boils  at  about 

Methyl  Hydride,  or  Methane.  CH3,H  =  CH4  [a  gas] 

Ethyl                        or  Ethane.  C2H6,H  =  CjH6  [a  gas] 

Propyl          "          or  Propane.  C3H7,H  =  C3H8  -30° 

Butyl                        or  Butane.  C4H9,H  -  C4H]0  0 

Amyl            "          or  Pentane.  C5Hn,H  =  C5Hi2  30 

Hexyl           "          orHexane.  C6Hi3,H  =  C6Hi4  60 

Heptyl                     or  Heptane.  C7H]5,H  =  C7Hi6  90 

Octyl            "          or  Octane.  C8H17,H  =  C8Hi8  120 

Nonyl                     orNonane.  C9Hi9,H  =  C9H20  150 

It  will  be  observed,  that,  while  each  member  differs  from  the  pre- 
ceding one  by  CHg,  there  is  a  difference  of  about  30°  in  the  boil- 
ing-points of  successive  members.  Many  of  the  hydrocarbons  of  this 
series  occur  in  the  "  coal-oil "  obtained  by  distilling  bituminous  coals 
and  shales  at  low  temperatures,  and  also  in  petroleum. 

222.  Petroleum  (literally,  rock-oil)  is  a  not  uncommon  natural 
product  found  in  various  parts  of  the  world.     In  some  cases  it 
rises  to  the  surface  of  the  earth,  but  it  is  generally  obtained  by 
sinking  wells  into  the  rock  strata  in  which  it  occurs.     On  this 
continent  it  is  already  found  in  large  quantities  in  Pennsylvania 
and  in  Canada.     In  some  of  the  wells  the  oil  rises  to  the  sur- 
face, being  forced  out  by  the  marsh-gas  which  accompanies  it ; 
in  other  cases,  the  oil  does  not  reach  the  surface,  and  must  be 
pumped  out. 

223.  Petroleum  is  a  thick,  greenish,  oily  liquid  of  somewhat 
varying  composition.     The  Pennsylvania  petroleum  is  mainly  a 
mixture  of  hydrocarbons  of  the  marsh-gas  series  from  C4H10  to 
CgHjjo,  together  with  other  hydrocarbons  of  high   boiling-point 
belonging  to  the  so-called  olefiant  gas  series  (§  259).     Marsh- 


METHYL  HYDRIDE  —ALCOHOL.  143 

gas  itself,  as  has  been  stated,  accompanies  petroleum,  and  in 
some  localities  it  issues  from  the  ground  in  such  large  quantities 
that  it  is  used  for  illuminating  purposes.  The  town  of  Fredonia, 
in  the  State  of  New  York,  has  thus  been  supplied  with  natural 
gas  for  some  years. 

224.  Just  as  marsh-gas  was  regarded  as  the  hydride  of  a  radical 
methyl  (CH3),  so  the  other  members  of  the  series  may  be  regarded 
as    hydrides   of  other    radicals,   ethyl    (C2H5),   propyl  (C3H7),   etc. 
These  radicals  are  univalent  (§  154),  and  when  they  are  obtained  in 
the  free  state,  they  form  molecules  built  on  the  type  of  free  hydrogen 
(H2)  :   thus  free  ethyl  is  (C2H5)2.     Besides  forming  hydrides,  these 
radicals  enter  into  a  variety  of  other  compounds  in  which  they  re- 
place hydrogen  atom  for  atom.     Among  these  compounds  are  the 
hydrates.     These  hydrates  are  formed  on  the  type  of  water  and  corre- 
spond in  formula  to  the  hydrates  of  sodium  and  potassium,  bodies 
already  somewhat  familiar. 

Water.  Potassium  hydrate.  Ethyl  hydrate. 

si°        HJO        (C!HS)I° 

The  hydrates  of  these  radicals  may  be  obtained  from  the  hydrides  in 
a  somewhat  indirect  manner  ;  they  are,  however,  ordinarily  obtained 
from  other  sources,  as  will  appear  hereafter.  Ethyl  hydrate  is  ordinary 
alcohol  (the  formula,  (C2H5)  HO,  representing  the  strongest  or'abso- 
lute  alcohol).  We  now  proceed  to  learn  something  of  the  preparation 
and  properties  of  this  important  derivative  of  one  of  the  members  of 
the,  marsh-gas  series. 

225.  Alcohol  (C2H5,HO).  —  When  the  juices  of  plants  or 
of  fruits  containing  sugar,  such  as  the  juice  of  the  grape,  are 
kept  for  some  time  at  a  temperature  of  20°,  a  peculiar  change 
takes  place.     The  liquor  begins  to  work,   bubbles  of  carbonic 
acid  (CO.,)  are  given  off,  and  it  will  be  found,  finally,  that  the 
sweet  taste  of  sugar  has  disappeared,  and  that  the  solution  now 
has  a  new  smell  and  taste ;  by  the  fermentation,  the  sugar  has 
been    converted   into    carbonic    acid    and    alcohol.      The   same 
change  may  be  brought  about  in  a  simple  solution  of  grape- 
sugar  under  the  influence  of  yeast  (Exp,  79,  §  193). 

is  a  collection  of  organized  bodies,  a  sort  of  fungus  or  low 


144  YEAST.— FORMATION  OF  ALCOHOL.  [§  226. 

form  of  vegetable  life.  This  fungus  is  made  up  of  cells  which  grow 
and  multiply  in  the  fermenting  liquid,  and  its  existence  in  a  liquid 
seems  to  be  a  necessary  condition  of  fermentation.  The  apparently 
spontaneoas  fermentation  which  takes  place  in  the  juice  of  fruits  is 
explained  by  supposing  that  the  spores  or  germs  of  such  a  plant  are 
introduced  from  the  air,  the  decay  of  certain  albuminous  matters  in 
the  juice  furnishing  favorable  conditions  for  the  reception  and  growth 
of  the  fungus. 

226.  Alcohol  is  a  colorless,  volatile  and  inflammable  liquid, 
lighter  than  water  and  capable  of  mixing  with  it  in  all  pro- 
portions. 

The  volatility  and  inflammability  of  alcohol  have  already  been 
illustrated  in  Exp.  84,  §  202.  The  production  of  alcohol  as  a  result 
of  fermentation  may  be  illustrated  by  a  repetition  of  Exp.  79,  §  193 
under  somewhat  different  conditions,  as  follows  :  — 

Exp.  100.  —  Dissolve  30  grms.  of  grape 
sugar  in  400  c.  c.  of  water,  and  with  the 
solution  fill  a  flask  of  350  or  400  c.  c. 
capacity  nearly  to  the  neck.  Add  two 
or  three  teaspoonfuls  of  fresh  brewers'  or 
bakers'  yeast,  and  then  connect  the  flask 
with  a  bottle  filled  with  water,  as  repre- 
sented in  Fig.  55.  .Put  the  whole  appa- 
ratus in  a  warm  place.  Fermentation  will  soon  set  in,  and  bubbles 
of  carbonic  acid  will  be  seen  rising  through  the  liquid.  As  this  gas 
collects  in  the  upper  part  of  the  flask,  it  will  pass  over  into  the  snjall 
bottle,  and  force  out  a  corresponding  amount  of  water.  When  the 
bottle  is  full  or  partly  full  of  the  gas,  remove  the  stopper,  and  prove 
the  presence  of  carbonic  acid  either  by  means  of  a  burning  match, 
which  will  be  extinguished  (Exp.  76,  §  190)  or  by  means  of  lime-water, 
which  will  be  rendered  turbid  (Exp.  73,  §  188).  Allow  the  liquid  in 
the  flask  to  remain  in  a  warm  place  for  about  48  hours,  when  the 
sweet  taste  of  the  sugar  will  be  found  to  have  wellnigh  disappeared 
as  the  sugar  will  have  been  converted  mainly  into  alcohol  and  car- 
bonic acid. 

This  experiment  may  be  performed  equally  well  by  substituting  45 
or  50  grms.  of  sirup  for  the  30  grms.  of  grape  sugar. 

227.  To  separate  the  alcohol  from  the  liquid  in  which  it  has 


§  227.] 


BY  FERMENTATION  OF  SUGAR. 


145 


been  formed  by  fermentation,  the  liquid  is  subjected  to  distilla- 
tion. The  boiling-point  of  alcohol  is  about  20°  lower  than  that 
of  water,  and  consequently  all  the  alcohol  will  be  found  in  the 
first  portion  of  the  distillate.  By  several  successive  distillations 
the  alcohol  may  be  obtained  nearly  pure. 

Exp.  101.  —  Pour  off  one-half  of  the  fermented  liquor  of  Exp.  100, 
and  reserve  it  for  Exp.  106  ;  with  the  remainder  proceed  as  follows  : 
Support  the  flask  on  the  iron  lamp-stand,  and,  by  means  of  a  delivery- 
tube  of  No.  6  glass,  connect  it  with  a  second  flask  capable  of  holding 
one-third  of  the  liquid  and  placed  on  a  water-bath,  as  represented 
in  Fig.  56.  From  this  Fig.  56. 

second  flask  a  delivery- 
tube  is  carried  to  a  small 
flask  kept  cool  by  im- 
mersion in  cold  water. 
Heat  the  liquid  in  the 
largest  flask,  so  that  it 
just  boils  :  the  vapor  of 
alcohol,  together  with  a 
certain  amount  of  steam, 
passes  into  the  second 
flask,  which  is  kept  just 
below  the  boiling-point  of  water  by  being  supported  on  the  water- 
bath  in  which  the  water  barely  boils.  At  this  temperature  a  con- 
siderable portion  of  the  alcohol,  together  with  some  water,  passes 
over  into  the  third  flask,  where  it  is  condensed.  Continue  the  opera- 
tion until  about  one-third  of  the  liquid  has  passed  out  of  the  large 
flask.  The  liquid  obtained  in  the  third  flask  is  a  dilute  alcohol  ;  the 
odor  of  alcohol  is  distinctly  perceptible,  but  the  akohol  may  not  be 
strong  enough  to  burn.  In  that  case  support  the  third  flask  on  the 
wire-gauze  over  the  lamp,  and  connect  it  by  means  of  a  delivery-tube 
with  another  small  flask,  which  is  kept  cool.  Heat  the  contents  of 
the  flask  gently  until  they  just  boil,  and  transfer  the  first  teaspoonful 
of  the  liquid  which  condenses  in  the  cooled  flask  to  a  porcelain  dish. 
If  the  experiment  has  been  successfully  conducted,  the  alcohol  thus 
obtained  will  be  strong  enough  to  take  fire  if  a  flame  be  brought  into 
contact  with  it. 

The  alcohol  obtained  by  successive  distillations  of  a  dilute 
alcoholic  liquid  still  retains  a  certain  amount  of  water.     This 
13 


146 


FRACTIONAL   DISTILLATION. 


[§  228. 


water  may  be  removed  by  adding  quick-lime,  a  substance  which 
has  a  great  attraction  for  water,  and  distilling  the  mixture. 
Alcohol  perfectly  anhydrous  is  called  absolute  alcohol.  Ex- 
posed to  the  air,  it  attracts  moisture.  Ordinary  strong  alcohol 
contains  about  10  per  cent  of  water. 

228.  Exp.  101  affords  an  excellent  example  of  what  is  known  as 
fractional  distillation.  When  the  boiling-points  of  several  liquids 
differ  by  a  considerable  number  of  degrees,  they  may  thus  be  sepa- 
rated from  each  other  in  a  tolerable  state  of  purity  by  observing  the 
temperature  of  the  boiling  liquid  and  collecting  by  themselves  the 
successive  portions  of  the  distillate  which  come  off  within  certain 
narrow  limits  of  temperature.  In  operating  with  very  volatile  liquids, 
it  is  well  to  interpose  a  cooling  apparatus  between  the  retort,  or  still, 
and  the  receiver.  Fig.  57  contains  a  representation  of  the  so-called 
Liebig's  condenser  alluded  to  in  §  32. 

Fig.  57. 


The  manufacture  of  burning  oil  from  crude  petroleum  is  another 
example  of  fractional  distillation.  When  petroleum  is  distilled,  the 
first  portion  of  the  distillate  consists  of  very  volatile  hydrocarbons 
known  by  the  general  name  of  naphtha.  The  less  volatile  compounds 
which  next  follow  form  the  "  kerosene  oil "  or  "  petroleum  oil "  of  com- 
merce. The  frightful  accidents  arising  from  the  use  of  kerosene  are 
due  to  the  fact  that  the  oil  is  often  imperfectly  freed  from,  or  pur- 
posely adulterated  with,  the  more  volatile  and  inflammable  hydro- 
carbons. All  these  volatile  hydrocarbons  in  the  state  of  vapor  form 
explosive  mixtures  with  air  j  and  such  explosive  mixtures  are  likely 


§  229.] 


FRACTIONAL  CONDENSATION.  —  ALCOHOL. 


to  be  formed  in  vessels  or  in  lamps  only  partially  full  of  the  volatile 
liquids. 

A  modification  of  this  process,  "  fractional  condensation,"  effects 
a  more  complete  separation.  In  this  process  the  vapors,  after  leaving 
the  retort,  pass  upwards  through  an  inverted  "  worm,"  the  tempera- 
ture of  which  is  so  regulated  that  the  less  volatile  bodies  are  almost 
entirely  condensed,  and  so  made  to  How  back  into  the  retort  ;  while 
the  more  volatile  vapors  go  forward,  and  are  condensed  in  the  usual 
way  in  appropriate  receivers. 

Fig.  58. 


229.  Alcohol  is  much  used  in  the  arts  ;  it  forms  the  basis  of 
all  fermented  and  distilled  liquors ;  it  is  employed  as  a  conven- 
ient fuel,  and,  when  mixed  with  benzol,  oil-  of  turpentine  or 
other  hydrocarbons,  for  the  production  of  light.  '  It  is  also 
valuable  as  a  solvent ;  it  dissolves  many  substances  such  as 
resins  and  oils,  which  are  insoluble  in  water  :  -thus,  shellac-var- 
nish is  an  alcoholic  solution  of  a  peculiar  resin  known  as  shellac  ; 
the  tinctures  of  pharmacy  are  alcoholic  solutions  of  medicinal 
principles. 

The  formula  of  absolute  alcohol  is  C2H6O.  It  may  be  regarded, 
as  has  been  said,  as  a  hydrate  of  the  radical  ethyl  (C2H5),  and  may 
be  written  (C2H5)  HO.  As  alcohol  is  a  hydrate  of  ethyl,  so  there 


148  ALCOHOLS.  — ETHER.  [§230. 

are  hydrates  of  each  of  the  radicals  of  the  marsh-gas  series  (§  221)  ; 
thus  :  — 

Boiling-point- 

Methyl  Alcohol  is  CH3,HO  or  CH4O,  66.5° 

Ethyl  "  "   C2H5,HO   "    C2H6O,  78.4 

Propyl         «  "  C3H7,HO   "    C3H8O,  97 

Butyl  «  "  C4H9,HO   "   C4H10O,  116 

Amyl  «  «  C5HU,HO  «    C6H12O,  137 

Etc. 

230.  Methyl  Alcohol  (CH3,HO)  resembles  ordinary  (ethyl) 
alcohol  in  being  a  light,  colorless,  inflammable  liquid.     It  resem- 
bles alcohol  also  in  its  solvent  powers,  and  is  used  in  its  stead 
for  many  purposes,  such  as  dissolving  shellac.     It  is  prepared  by 
the  destructive  distillation  of  wood  (§  282),  and  ordinarily  con- 
tains certain  impurities,  which  give  to  it  an  empyreumatic  odor. 
It  is  commonly  known   as  wood-spirit.     Methylated   spirit    is 
ordinary  alcohol,  to  which  a  certain  amount  of  methyl  alcohol 
has  been  added  ;  this  addition  does  not  interfere  with  the  use  of 
the  alcohol  for  many  purposes  to  which  it  is  applied  in  the  arts, 
but  renders  it  unfit  for  drinking. 

231.  Amyl  Alcohol  or  Fusel  Oil  (C5Hn,HO)  is  a  colorless 
liquid  of  disagreeable  odor.     It  will  not  mix  with  water,  and  is 
not  readily  inflammable.     It  is  formed  in  the  manufacture  of 
brandy  and  whiskey  from  potatoes  and  grain,  and,  as  it  has 
a  boiling-point  much  higher  than  that  of  ordinary  alcohol,  it 
may  be  separated  from  alcohol  quite  completely  by  the  method 
of   fractional  distillation.      Fusel   oil  burns  with   a  somewhat 
smoky  flame,  and  is  principally  used  for  purposes  of  illumina- 
tion. 

232.  Ether.  —  When  a  mixture  of  strong  sulphuric  acid  and 
alcohol  is  heated  in  a  retort,  there  distils  over  with  water,  a 
highly  volatile,  inflammable  liquid  known  as  ether.     The  distil- 
late, which  must  be  condensed  in  a  well-cooled  receiver,  sepa- 
rates into  two  layers ;  the  ether  being  almost  insoluble  in  the 
water  and  lighter  than  it,  forms  the  upper  layer,  and  may  be 
drawn  off   nearly  free  from  water.     The  last  portions  of  water 
are  removed  by  allowing  the  ether  to  stand  over  quick-lime,  and 
then  distilling. 


§234.]  ETHER.  —OXIDE   OF  ETHYL.  149 

The  reaction  between  the  sulphuric  acid  and  alcohol  may  be  rep- 
resented as  taking  place  in  two  stages  :  — 

(1.)     (C2H5;HO  +  H2S04  =  HVC2H5)SO4  +  H2O. 

Alcohol.  Sulphuric          Hydrogen  Ethyl          Water. 

acid.  sulphate. 


(2.)     H(C2H3)S04  +  (C2H5)HO  =  (C2H5)2O 

Hydrogen  Ethyl      »       Alcohol.  Ether.  Sulphuric 

sulphate.  acid. 

The  alcohol  and  sulphuric  acid  are  mixed  in  equivalent  propor- 
tions, and  as  the  water  and  ether  distil  off,  the  loss  is  supplied  by  a 
.stream  of  fresh  alcohol  flowing  slowly,  but  without  interruption,  into 
the  retort.  The  operation  thus  goes  on  continuously. 

Exp.  102.  —  Into  a  small  test-tube  put  10  drops  of  ordinary  alco- 
hol and  as  much  strong  sulphuric  acid,  and  heat  the  mixture  gently 
over  the  lamp.  Ether  will  be  formed,  and  may  be  recognized  by  its 
peculiar  odor. 

The  student  should  never  attempt  to  perform  any  experiment 
requiring  more  than  a  very  minute  quantity  of  ether,  since  it  is 
highly  dangerous  to  work  with  this  substance  on  account  of  its  great 
volatility,  and  ready  inflammability. 

233.  Ether  is  a  colorless,  very  mobile,  volatile  liquid  :  it  pos- 
sesses a  powerful  odor,  and,  when  inhaled,  produces  insensibility 
to  pain  ;  hence  it  is  used  in  surgical  operations.     The  vapor  of 
ether  is  very  heavy  and  exceedingly  inflammable,  and  in  certain 
proportions  forms  an  explosive  mixture  with  air. 

Exp.  103.  —  Pour  a  small  quantity  of  ether  into  the  palm  of  the 
hand,  and  observe  the  rapidity  with  which  it  evaporates,  and  also  the 
cold  produced  by  this  evaporation. 

Exp.  104.  —  Into  a  tumbler  or  other  very  wide-mouthed  vessel 
put  a  few  drops  of  ether.  Cover  the  vessel  loosely,  and  allow  to 
stand  for  a  few  moments  ;  then  bring  a  lighted  match  to  the  mouth 
of  the  vessel  :  the  heavy  vapor  of  ether  will  have  displaced  the  air 
in  the  vessel,  and  will  take  fire  at  the  mouth  of  the  vessel  with  a 
sudden  flash. 

234.  Ordinary  ether  ((C2H5)2O)  is  an  oxide  of  the  radical  ethyl 
(C2H5).      The    corresponding   oxides    of   the   other  radicals   of    the 
marsh-gas   series   are  classed  together  under  the  general  name   of 
ethers  ;  thus  :  — 


150  ETHERS.  —  MERC  APTANS.   '  [§  234. 

Methyl  oxide  or  Methyl  Ether  is  (CH3)2O  or  C2H6O 

Ethyl          "  "   Ethyl          "  u  (C2H5)2O  "   C^H10O 

Propyl        "  "    Propyl        «  «  (C3H7)2O  «   C6HUO 

Butyl          "  "    Butyl  "  "  (C4H9)2O  "    C8H18O 

Etc. 

As  these  hydrocarbon  radicals,  methyl,  ethyl,  propyl,  etc,,  unite 
with  hydrogen  to  form  hydrides,  with  oxygen  to  form  oxides  (ethers), 
and  with  hydrogen  and  oxygen  to  form  "hydrates  (alcohols),  so  they 
can  form  salts  corresponding  to  the  various  acids.  The  formulae  of 
these  salts  may  be  written  by  replacing  the  hydrogen  of  the  acid  by 
the  different  radicals.  Thus  ethyl  sulphate  is  (C2H.)2SO4  ;  ethyl 
nitrate  is  (C2H5)NO3  ;  methyl  chloride  is  CH3C1  ;  propyl  sulphide 
is  (C3H7)2S  ;  and  so  on.  In  the  case  of  an  acid  like  H2SO4  con- 
taining two  replaceable  atoms  of  hydrogen,  there  can  be  formed  bodies 
like  hydrogen  ethyl  sulphate  H(C2H.)SO4  corresponding  precisely 
to  hydrogen  potassium  sulphate,  HKSO4. 

Mercaptans.  —  Among  the  compounds  of  the  radicals  of  the  marsh- 
gas  series,  may  be  mentioned  the  mercaptans.  These  compounds 
correspond  in  formula  to  the  alcohols,  except  that  the  oxygen  is  re- 
placed by  sulphur  :  they  may  be  regarded  as  derived  from  hydrogen 
sulphide,  in  the  same  way  that  alcohol  is  derived  from  water. 

Water.  Ethyl  alcohol.        Hydrogen  sulphide.         Ethyl  mercaptan. 

H 


Q 

H  H  H  <  Hi 

The  salts  of  the  various  radicals  are  often  called  compound 
ethers  ;  methyl  chloride  is  called  methyl-chlorhydric  ether,  ethyl 
sulphate  is  called  ethyl-sulphuric  ether,  or  simply  sulphuric  ether. 
(The  term  "  sulphuric  ether  "  is  sometimes  used  to  denote  ordinary 
(ethyl)  ether.  This  designation  is,  however,  improper,  as  ordinary 
ether  contains  no  sulphur  whatever.)  Several  of  these  compound 
ethers  are  manufactured  in  large  quantities  for  the  preparation  of 
perfumery  and  flavoring  extracts.  Thus  amyl  acetate,  or  amyl-acetic 
ether  (made  from  fusel  oil),  has  the  odor  and  taste  of  the  jargonelle 
pear  ;  amyl  valerianate  has  the  smell  and  taste  of  apples,  and  is 
known  as  apple-oil  ;  ethyl  butyrate  has  the  flavor  of  pine-apples,  etc. 

The  preparation  of  one  of  these  compound  ethers,  ethyl  acetate, 
may  be  illustrated  by  the  following  experiment. 

Exp.  105.  Into  a  small  test-tube  put  10  drops  of  ordinary  alcohol, 
and  the  same  amount  of  strong  sulphuric  acid.  Add  a  crystal  of 
sodium  acetate  as  large  as  a  small  pea,  and  heat  the  mixture  gently. 


§235.] 


ACETIC  ACID.— VINEGAR. 


151 


Acetic  ether,  ethyl  acetate,  is  formed,  and  may  be  recognized  by  its 
peculiar  odor. 

235.  Acetic  Acid  (C2H4O2). — When  the  alcoholic  liquid 
formed  by  the  fermentation  of  the  juice  of  grapes  or  other 
fruits  is  exposed  to  the  air,  it  gradually  becomes  sour,  and  is 
eventually  converted  into  vinegar.  Under  the  influence  of  the 
oxygen  of  the  air,  the  alcohol  changes  into  acetic  acid.  Vine- 
gar is  a  very  dilute  solution  of  this  acid,  containing  about  2  to  4 
per  cent  of  the  acid,  together  with  coloring  matter,  and  various 
other  impurities  derived  from  the  juice  of  the  fruit  from  which 
it  is  prepared. 

Exp.  106.  —  Allow  that  portion  of  the  alcoholic  liquor  of  Exp. 
100  which  was  not  distilled  to  remain  for  a  number  of  days  in  a 
loosely-covered  vessel.  The  liquid  will  gradually  become  sour,  and 
acquire  the  taste  and  smell  of  vinegar.  The  alcohol  has  been  con- 
verted into  acetic  acid.  Preserve  this  acid  liquid  for  use  in  a  sub- 
sequent experiment. 

Vinegar,  as  has  just  been  seen,  may  be  produced  by  allowing  an 
alcoholic  liquid  to  become  sour  gradually,  by  exposure  to  the  air  in 
imperfectly-closed  vessels.  On  the  large  scale,  however,  it  is  gen- 
erally made  by  allowing  the  air  to  have 
access  to  weak  alcohol,  spread  in  a  very 
thin  layer  over  a  very  great  surface. 
The  operation  is  conducted  in  large 
casks  filled  with  wood-shavings,  over 
which  the  alcoholic  liquid  (as  cider, 
whiskey  or  brandy  diluted  with  water) 
slowly  trickles.  The  cask  is  furnished 
with  a  false  bottom,  and  with  a  head 
perforated  with  small  holes,  which  serve 
to  distribute  the  alcohol  evenly  over  the 
shavings.  Air  enters  the  cask  through 
holes,  as  at  a,  and  escapes  through 
the  tubes  (c  c  c),  and  through  several 
holes  in  the  cover  of  the  cask.  The 
liquid  which  runs  out  of  the  cask  may 
be  returned  to  the  top,  until,  after  passing  through  the  cask  several 
times,  the  alcohol  is  entirely  converted  into  acetic  acid.  The  cask 
may  be  made  of  such  size,  and  the  flow  so  regulated,  that  the  con- 
version of  the  alcohol  to  vinegar  is  complete  after  one  operation. 


Fig.  59. 


152  ALDEHYDE.  —  FATTY  AC/D  SERIES.  [§236. 

The  chemical  changes  which  take  place  are  as  follows  :  the  alco- 
hol under  the  influence  of  a  little  yeast,  honey  or  grape  sugar,  with 
which  it  is  mixed,  has  a  great  tendency  to  absorb  oxygen  from  the  air, 
and  be  converted  into  water,  and  a  new  compound,  aldehyde. 

C2H5,HO  +  O  =  C2H30,H  -f  H20. 

Alcohol.  Aldehyde. 

Aldehyde  is  an  unstable  compound  which  oxidizes  very  readily. 
As  it  passes  over  the  shavings,  the  oxygen  of  the  air  comes  in  contact 
with  it  over  a  very  great  surface,  and  it  is  rapidly  converted  into 

acetic  acid  : 

C2H30,H  -f  O  =  C2H30,HO. 

Aldehyde.  Acetic  acid. 

Aldehyde  is  a  very  volatile  compound,  and.  on  this  account,  unless  the 
supply  of  air  furnished  be  abundant,  a  considerable  loss  of  alcohol  is 
experienced  in  this  process. 

236.  Chloral  or  Trichloraldehyde  (C2C13OH).  —  By  replacing 
three  atoms  of  hydrogen  in  the  formula  of  aldehyde  by  as  many 
atoms  of  chlorine,  the  formula  of  a  body  known  as  chloral  is  ob- 
tained.     This   compound    is  formed  by   passing   chlorine   through 
absolute  alcohol.     It  is  an  oily  fluid,  which  unites  with  a  small  quan- 
tity of  water  to  form  a  crystalline  hydrate,  much   used  of  late  in 
medicine  to  induce  sleep. 

237.  The  formula  of  acetic  acid  is   C2H4O2  or,  written  on  the 

type  of  water,      2-,3     >  O,  an  atom  of  hydrogen  being  replaced  by 

a  hypothetical  oxygenated  radical,  C2H3O,  called  acetyl.  This 
radical  has  not  been  isolated  :  its  chloride,  however,  is  known.  If 
this  hypothetical  radical  acetyl,  C2H3O,  1  e  compared  with  ethyl, 
C2H5 ,  it  will  appear  that  two  atoms  of  hydrogen  in  the  latter  are  rep- 
resented by  one  atom  of  oxygen  in  the  former.  By  the  similar  device 

from  may  be  derived          the  hypothetical  radical  of 

Methyl  CH3  Formyl  CHO  Formic  acid  CH.O., 
Propyl  CSH7  Propionyl  C3H5O  Fropionic  acid  C.HGO, 
Butyl  C4H9  Butyryl  C4H.O  Butyric  acid  C4HSO, 
Amyl  C-H'u  Valeryl  C,U,O  Valeric  acid  C.H10O2 

Etc.  Etc.  Etc. 

Acetic  acid  is  thus  one  member  of  a  series  of  acids  ;  they 
are  called  the  fatty  acids,  and  several  members  of  the  series  are 
of  very  great  industrial  importance. 

238.  Acetic  acid  is  one  of  the  products  of  the  distillation 


§239.]  ACETIC  ACID.— FORMIC  ACID.  153 

of  wood  (§  282),  and,  thus  obtained,  it  is  known  in  the  crude 
state  as  pyroligneous  acid. 

The  pure  acid  is  obtained  by  acting  on  some  acetate,  as  sodium 
acetate,  with  sulphuric  acid,  and  then  distilling  the  mixture. 
At  the  ordinary  temperature,  acetic  acid  is  a  volatile  liquid 
possessing  a  pungent  odor,  but  at  17°  it  becomes  a  transparent 
solid ;  hence  the  name  glacial  acetic  acid  applied  to  the 
strongest  acid. 

Exp.  107.— To  the  acid  liquid  of  Exp.  106,  or  to  40  or  50  c.  c. 
of  common  vinegar,  add  powdered  chalk  (calcium  carbonate)  as  long  as 
the  addition  causes  effervescence.  Calcium  acetate  is  formed  and 
remains  dissolved  in  the  liquid.  Filter  the  solution,  and  evaporate 
the  nitrate  to  dryness  at  a  gentle  heat.  The  solid  residue  is  an  im- 
pure calcium  acetate.  Place  a  portion  of  this  calcium  acetate  in  a 
small  test-tube,  and  heat  gently  with  a  few  drops  of  strong  sulphuric 
acid.  Acetic  acid  will  be  set  free,  and  may  be  recognized  by  its  pecu- 
liar odor.  If  ordinary  vinegar  be  used  in  this  experiment,  it  will  be 
better  to  decolorize  the  solution  of  calcium  acetate  by  mixing  it  with 
powdered  bone  black  before  filtering  (see  Exp.  72,  §  185). 

The  acetates  are  important  bodies,  and  many  of  them  are  used 
in  the  arts  and  in  medicine.  Aluminum  acetate  is  used  in  dyeing 
(§  451)  ;  lead  acetate  is  familiar  under  the  name  of  sugar  of  lead  ; 
copper  acetate  is  known  as  verdigris  ;  ethyl  acetate  is  acetic  ether. 

239.  Formic  acid  (CH2O2),  another  member  of  the  fatty 
acid  series,  is  secreted  by  ants,  and  was  first  obtained  by  dis- 
tilling the  bodies  of  these  insects  :  it  bears  the  same  relation  to 
methyl  alcohol  (CH4O)  that  acetic  acid  does  to  ordinary  (ethyl) 
alcohol,  and  may  be  prepared  by  the  oxidation  of  methyl  alco- 
hol. Formic  acid  is  interesting  because  one  of  its  salts,  potas- 
sium formate,  may  be  readily  prepared  from  what  are  usually 
classed  as  inorganic  substances. 

If  moist  caustic  potash  be  exposed  to  carbon  protoxide  at  a  tem- 
perature of  100°,  the  gas  is  slowly  absorbed,  and  potassium  for- 
mate is  produced  :  from  potassium  formate  thus  made  the  acid  itself 
may  be  indirectly  obtained. 

TT  )  TT     ) 

f  o         -I-         co  !  o 

H  (  (CHO)  J 

Potassium  hydrate.  Carbon  protoxide.  Potassium  formate. 


154  NATURAL  FATS  AND   OILS.  [§  240. 

Formic  acid  is  one  of  a  vast  number  of  compounds  which 
formerly  were  supposed  to  be  produced  only  through  the  agency 
of  living  organisms,  but  which  now  can  be  made  in  the  labora- 
tory from  inorganic  substances.  This  synthetical  construction 
of  so-called  organic  substances  has  contributed  to  obscure  the 
distinction  formerly  drawn  between  organic  and  inorganic  chem- 
istry. 

240.  One  of  the  salts  of  formic  acid  will  serve  as  an  excellent 
illustration  of  the  value  of  rational  formulae  (§  152).  The  formula  of 
methyl  formate  (C2H4O2)  is  the  same  as  that  of  acetic  acid, 
and  the  empirical  formulae  afford  no  means  of  distinguishing  be- 
tween these  two  substances  ;  if,  however,  methyl  formate  be  written 


°  and  acetic  acid>  as  Before,  O   these   formulae 

a.       ) 

represent  to  the  mind  two  distinct  bodies.  As  the  properties  of  the 
two  substances  are  very  different,  we  naturally  seek  to  account  for 
such  different  manifestations  of  the  same  elements  in  the  same  pro- 
portions by  imagining  some  difference  in  the  arrangement  of  the 
atoms  within  the  molecule  ;  and,  although  we  cannot  know  what  this 
arrangement  is,  we  can  recall  by  the  rational  formulae  some  of  the 
reactions  which  occur  in  the  formation  or  the  decomposition  of  the 
substances  in  question.  Bodies  which  like  acetic  acid  and  methyl 
formate  have  the  same  ultimate  composition  are  called  isomeric. 

Other  acids  of  the  fatty  acid  series  will  be  brought  to  our 
notice  by  the  study  of  a  very  important  natural  group  of  organic 
compounds,  that  of  the  fats  and  oils. 

241.  Natural  Fats  and  Oils,  —  The  various  fats  and  non- 
volatile oils  obtained  from  both  the  animal  and  the  vegetable 
kingdom  are  in  the  main  mixtures  of  three  well-defined  bodies, 
two  of  which,  stearin  and  palmitin,  are  solid  at  the  ordinary 
temperature,  while  the  third,  olein,  is  liquid. 

Exp.  108.  —  Expose  a  test-tube  full  of  olive-oil  to  cold  by  sur- 
rounding it  with  a  mixture  of  salt  and  pounded  ice.  A  portion  of  the 
oil  solidifies,  while  another  portion  remains  liquid.  The  solid  portion 
is  mainly  palmitin,  the  liquid,  olein. 

Olive  oil  consists  essentially  of  olein  and  palmitin  ;  beef-tal- 
low is  mainly  stearin  ;  lard  is  made  up  of  olein  and  palmitin  ; 


§  243.1  MANUFACTURE  OF  SOAP.  155 

butter  is  olein,  palmitin,   together  with  several  other  peculiar 
fats,  to  which  its  taste  and  odor  are  due. 

The  chemical  constitution  of  these  bodies  may  be  best  represented 
by  the  use  of  typical  formulae.  Stearin  is  a  salt  of  stearic  acid,  and 
may  be  regarded  as  built  upon  the  type  of  three  molecules  of  water  : 
its  formula  may  be  derived  from  that  of  stearic  acid  by  substituting 
for  three  atoms  of  hydrogen  in  three  molecules  of  the  acid  one  atom 
of  the  trivalent  radical  glyceryl  (C3H5),  thus  :  — 

Type.  Stearic  aeid.  Stearin. 

(Three  molecules.)  (One  molecule.) 

H3  )  Q  (CW),  I  Q  (C18H350)3  ) 

H3|°3  H3        \°*  (C3H5)rs 

Stearin  is  glyceryl  stearate ;  similarly  palmitin  is  glyceryl 
palmitate,  and  olein  is  glyceryl  oleate.  Oleic  acid  does  not 
belong  to  the  same  series  with  stearic  and  palmitic  acids  ;  but,  from 
the  association  in  nature  of  the  oleates  and  the  stearates,  it  is  con- 
veniently introduced  in  this  connection. 

242.  The  various  fats  and  oils  are  insoluble  in  water ;  they 
are,  however,  readily  dissolved  by  certain  liquids,  such  as  ether, 
benzol,  oil  of  turpentine,  etc. 

Exp.  109.  —  Fill  a  small  bottle  half  full  of  water,  and  pour  in  a 
few  drops  of  olive-oil.  The  oil  remains  on  the  top  of  the  water,  and 
is  not  dissolved  by  agitating  the  mixture. 

Exp.  110.  —  Into  a  small  bottle  put  two  teaspoonfuls  of  concen- 
trated ether,  and  add  one  quarter  as  much  olive-oil.  Cork  the  bottle 
tightly,  and  shake  it :  the  oil  is  readily  dissolved  by  the  ether. 

243.  Manufacture  of  Soap.  —  Very  great  industrial  impor- 
tance attaches  to  many  of  the  natural  fats  and  oils  on  account  of 
their  use  in  the  manufacture  of  soaps  and  "  stearine  "  candles  ; 
in  both  of  these  industries,   a  hydrate  of  glyceryl,  glycerin, 

3tr    I  O3,  is  a  secondary  product. 

H3    ) 

The  manufacture  of  soap  may  be  illustrated  by  the  following 
experiment  :  — 

Exp.  111.  —  Dissolve  15  grms.  of  solid  caustic  soda  in  120  c.  c.  of 
water.  When  the  suspended  impurities  have  settled  to  the  bottom 
of  the  solution,  pour  off  one  half  of  the  clear  liquor  into  a  deep  iron 


156  MAtfVFACTUhE  OF  SOAP.  [§244 

or  porcelain  dish  of  at  least  500  c.  c.  capacity  (see  Appendix,  §  21), 
add  an  equal  bulk  of  water,  and  50  grms.  of  beef  tallow.  Bring  the 
mixture  to  boiling  and  boil  it  steadily  for  three  quarters  of  an  hour, 
supplying  from  time  to  time  the  water  lost  by  evaporation  ;  then  add 
the  remainder  of  the  solution  of  caustic  soda,  and  continue  to  boil 
steadily  for  an  hour  or  more,  allowing  the  liquid  to  become  somewhat 
more  concentrated  towards  the  end  of  that  time  •  then  add  20  grms. 
of  fine  salt,  boil  for  a  minute  or  two,  and  allow  the  liquid  to  cool.  A 
part  of  the  mass  becomes  solid,  and  rises  to  the  top  ;  it  is  hard  soap. 

The  chemical  action  is  thus  explained  :  when  tallow  (glyceryl 
stearate  and  oleate)  is  boiled  with  sodium  hydrate,  there  is  formed  so- 
dium stearate  (and  oleate)  and  glyceryl  hydrate.  When  common  salt 
is  added,  the  soap  (sodium  stearate  and  oleate),  being  insoluble  in  the 
saline  liquid,  separates  as  a  solid.  The  liquid  remaining  contains  in 
solution  the  excess  of  sodium  hydrate  employed,  as  well  as  the  salt 
and  the  glycerin. 

Soap  may  be  made  more  quickly  by  using  castor-oil  instead  of  beef- 
tallow.  Mix  100  c.  c.  of  castor-oil  and  100  c.  c.  of  caustic  soda  solution 
prepared  as  above,  and  boil  for  30  minutes.  Then  add  150  c.  c.  of 
water,  bring  to  a  boil,  and  add  20  grms.  of  salt.  The  soap  rises  to  the 
top  and  may  be  removed  when  cold.  Castor-oil  is  mainly  glyceryl 
ricinoleate  ;  the  chemical  change  is  similar  to  that  just  described. 

Exp.  112. — Heat  some  of  the  soap  of  Exp.  Ill  with  soft  water.  A 
nearly  clear  solution  will  be  obtained  if  the  decomposition  of  the 
tallow  or  oil  was  complete.  Add  dilute  chlorhydric  acid  until  the 
solution  is  decidedly  acid.  The  liquid  will  become  turbid,  and  on 
standing,  will  become  covered  with  a  layer  of  a  fatty  substance  which 
is  a  mixture  of  stearic  and  oleic  acids  (or  mainly  ricinoleic  acid  if 
castor-oil  was  used).  The  sodium  chloride  formed  will  be  held  in 
solution  by  the  liquid. 

Other  bases  besides  caustic  soda  may  be  used  to  effect  the 
decomposition  of  oils  or  fats.  If  caustic  potash  be  used,  a  soft 
soap  is  formed  ;  if  slaked  lime  be  employed,  there  is  formed  a 
lime  soap,  calcium  stearate,  etc.,  insoluble  in  water ;  if  lead 
oxide  be  used,  there  results  an  insoluble  lead  soap  used  in  medi- 
cine under  the  name  of  lead  plaster  or  diachylon. 

244.  In  Exp.  Ill,  one  of  the  products  of  the  reaction,  gly- 
cerin, remained  dissolved  in  the  solution  of  sodium  chloride  and 
hydrate.  This  substance  may  be  prepared  as  follows  :  — 


§  245.]  GLYCEkltf.  —  XlTkO-GLYCEttlX.  157 

Exp.  113.  —  Into  a  deep  porcelain  dish  put  50  grms.  of  litharge 
and  75  c.  c.  water.  Into  this  mixture  stir  50  grins,  of  olive  oil,  and 
boil  the  mixture  steadily  for  50  or  60  minutes  with  constant  stirring, 
and  occasional  addition  of  water  to  replace  that  lost  by  evaporation. 
The  oil  is  gradually  decomposed ;  an  insoluble  lead  soap  (lead 
plaster)  is  formed,  and  the  color  of  the  mass  in  the  dish  becomes 
lighter.  When  the  oil  seems  to  be  entirely  decomposed,  pour  off  the 
liquid  portion  through  a  filter,  add  50  c.  c.  of  water  to  the  lead 
plaster,  boil  for  five  minutes,  and  pass  this  liquid  also  through  the 
filter.  The  glycerin  is  dissolved  by  the  water,  and  with  it  passes 
through  the  filter.  Evaporate  the  filtered  liquid  to  dryness  at  a  gen- 
tle heat  :  the  glycerin  will  remain  as  a  sirupy,  non-volatile  liquid, 
having  a  sweet  taste.  As  the  amount  of  glycerin  obtained  will  be 
very  small,  it  is  well  to  transfer  the  solution  when  nearly  evaporated 
to  a  watch-glass,  and  to  finish  the  evaporation  on  a  water-bath. 

Glycerin,  when  pure,  is  a  colorless,  sweet-tasting,  sirupy 
liquid,  which  mixes  with  water  in  all  proportions.  When 
heated  in  the  air,  it  is  slightly  volatile,  but  cannot  be  distilled 
without  decomposition,  and  the  formation  of  vapors  of  acrolein 
very  irritating  to  the  eyes.  This  same  substance  is  formed  when 
fat  burns,  and  is  the  cause  of  the  peculiar  odor  given  off'  from 
the  smouldering  wick  of  a  tallow  candle. 

Glycerin  is  used  somewhat  in  medicine,  mainly  for  external 
applications  :  its  use  depends  upon  the  fact  that  it  is  but  slightly 
volatile,  and  does  not  dry  up  or  undergo  change  when  exposed 
to  the  air. 

245.  Nitre-Glycerin.  —  If  glycerin  be  allowed  to  flow  grad- 
ually into  a  mixture  of  nitric  acid  and  oil  of  vitriol,  which  is 
kept  cool,  a  heavy  oily  liquid  collects  at  the  bottom  of  the  acid. 
It  is  known  as  nitro-glycerin,  and  is  a  highly  explosive  com- 
p  nmd,  being  decomposed  either  by  direct  application  of  heat,  or 
by  percussion.  It  is  used  for  blasting  purposes  instead  of  gun- 
powder, but  is  very  dangerous  to  transport  :  the  danger  in  using 
it  can  be  very  much  lessened  by  making  the  nitro-glycerin  im- 
mediately before  use  at  the  quarry  or  other  locality  where  it  is 
to  be  employed. 

The  formula  of  nitro-glycerin  is  ^    3    * '  (  O3,  while  that  of  gly- 

(NO2)3 ) 


158  SAPONIFICATION.  [§  246. 

cerin  is  '    3    5^  (  Q3 ;  that  is,  three  atoms  of  hydrogen  have  given  place 
H3   ) 

to  three  atoms  of  the  radical  nitryl  (NO2)  :  nitro-glycerin  may  be 
regarded  as  glyceryl  nitrate. 

246.  As  has  been  stated,  glycerin  is  also  a  product  of  the 
manufacture  of  what  are  known  as  stearine  candles.  These 
candles  are  not,  properly  speaking,  stearin,  but  are  made  of  the 
solid  fatty  acids  ;  namely,  stearic  and  palmitic.  Any  process  by 
which  stearin  (and,  of  course,  palmitin  and  olein)  is  decomposed, 
so  that  the  fatty  acid  or  glycerin,  or  both  bodies,  are  set  free,  is 
termed  saponification,  even  in  cases  where  no  soap  results  from 
the  reaction. 

By  treating  the  fat  with  sulphuric  acid,  it  may  be  decomposed 
with  formation  of  the  fatty  acids  and  glycerin,  and  the  two  pro- 
ducts can  be  readily  separated  from  each  other.  The  decomposi- 
tion may  also  be  effected  by  the  use  of  superheated  steam,  and 
in  the  manufacture  of  candles  these  two  methods  are  employed 
to  a  very  large  extent,  although  the  fatty  acids  are  sometimes 
obtained  by  first  forming  a  lime  soap  and  then  decomposing  it 
with  acid,  as  the  soda  soap  was  decomposed  in  Exp.  112,  The 
fatty  acids  are  cooled  and  submitted  to  pressure,  which  separates 
the  oleic  acid  :  the  solid  acids  are  then  moulded  into  proper  forms. 

Candles  are  also  manufactured  from  spermaceti,  paraffin  and  wax. 
Spermaceti  is  a  solid  fat  obtained  by  cold  and  pressure  from  the  oil  of 
the  sperm  whale  ;  when  saponified,  it  yields  palmitic  acid  and  ethal 
(C]6H34O).  Paraffin  is  at  ordinary  temperatures  a  white  solid  having 
a  pearly  lustre.  It  is  generally  regarded  as  a  mixture  of  several  mem- 
bers of  the  marsh-gas  series  of  hydrocarbons  (Cn  Hsnfs),  which, 
indeed,  are  sometimes  designated  as  the  paraffin  series  or  the  paraffins. 
It  occurs  in  petroleum,  and  when  the  petroleum  is  distilled,  it 
comes  off  in  abundance  at  the  latter  part  of  the  distillation.  It  is 
separated  from  the  accompanying  liquid  hydrocarbons  by  cold  and 
pressure.  Paraffin  also  occurs  in  smaller  quantity  among  the  products 
of  the  distillation  of  bituminous  coal  and  wood.  Beeswax  is  mainly 
a  salt  of  palmitic  acid,  melissyl  palmitate,  together  with  a  free  acid, 
cerotic  acid.  Chinese  wax,  produced  by  an  insect  belonging  to  the 
same  genus  as  the  cochineal  insect,  yields  on  saponification  two 
bodies,  cerotin  and  cerotic  acid  :  it  is  cerotyl  cerotate. 


§  249.]  VEGETABLE  OILS.  159 

247.  Artificial  Fats.  —  While  by  the  various  processes  of  saponi- 
fication  it  is  possible  to  obtain  from  the  natural  fats  (with  the  ele- 
ments of  water)  both  glycerin  and  a  fatty  acid,  it  has  also  been  found 
possible  to  reproduce  the  fats  by  bringing  the  fatty  acids  and  glycerin 
together  under  appropriate  conditions  :  in  this  case  water  is  elimi- 
nated precisely  as  water  was  set  free  in  the  formation  of  potassium 
nitrate  from  caustic  potash  and  nitric  acid  (Exp.  26,  §  60). 

Glycerin.  "  Stearic  acid.  Stearin.  Water. 

(C° H>  ( °-  +  3  [(CA H}  1  °  1  =  rc  H^  i  °-  +  3  H<° 

H3  }  L  H  )       J         (C^H^O^  ) 

248.  Vegetable  Oils.  —  Of  the  oils  and  fats  thus  far  con- 
sidered, all,  with  the  exception  of  olive  oil,  have  been  of  animal 
origin  :  all  plants,  however,  contain  some  representative  or  repre- 
sentatives of  this   class.      These  vegetable  fats  and  oils  occur 
most  abundantly  in  certain  seeds  and  fruits,  such  as  the  seeds  of 
hemp,  flax,  cotton,  sunflower,  and  the  kernels  of  the  stone  of 
the  peach,  also  in  such  nuts  as  the  peanut,  butternut,  beechnut, 
almond,  etc.     Oil  occurs  also  in  the  cereals,  as  may  be  illustrated 
by  the  following  experiment  :  — 

Exp.  114. — Dry  two  or  three  teaspoonfuls  of  corn-meal  on  the 
water-bath  for  an  hour  or  two.  Put  the  dry  meal  into  a  small  bottle 
and  pour  upon  it  twice  its  bulk  of  ether.  Cork  the  bottle  tightly  and 
shake  it  from  time  to  time  during  half  an  hour.  Finally  filter  the 
liquid  into  a  clean  porcelain  dish  (taking  care  that  there  is  no  lighted 
lamp  or  fire  in  the  vicinity),  and  place  the  dish  where  there  is  a  good 
draught.  The  ether  will  evaporate  spontaneously  and  a  yellowish 
oil  will  remain. 

All  of  these  oils  are  called  fixed  oils  :  they  leave  a  permanent 
greasy  stain  on  paper,  and  cannot  be  distilled  unchanged. 

The  fixed  vegetable  oils  consist  in  great  measure,  like  the  animal 
fats,  of  stearin,  olein  and  palmitin  ;  but  many  of  them  contain  other 
substances  in  greater  or  less  proportion.  Thus  bayberry-tallow,  a 
familiar  example  of  a  vegetable  fat,  consists  in  part  of  palmitin  and 
palmitic  acid,  and  in  part  of  a  substance  known  as  lauric  acid. 

249.  Drying  Oils.  —  Certain  oils,  especially  linseed  oil,  when 
exposed  to  the  air,  gradually  absorb  oxygen  and  become  solid. 
iSucti  oils  are  called  drying  oils.     This   absorption  of  oxvgen 


160 


ESSENTIAL   OILS.  — OIL   OF  CLOVES. 


[§  250. 


causes  the  evolution  of  a  considerable  degree  of  heat :  in  fact, 
cases  of  spontaneous  combustion "  often  occur  from  the  taking 
fire  of  heaps  of  rags,  tow  or  other  light  material,  saturated  or 
smeared  with  oil. 

250.  Essential  Oils.  —  To  be  distinguished  from  the  non- 
volatile or  fixed  oils  are  the  volatile  or  essential  oils.  These 
compounds,  in  some  points,  resemble  the  fixed  oils," —  they  are 
inflammable,  insoluble  in  water  and  readily  soluble  in  alcohol 
and  ether :  they  are,  however,  more  or  less  volatile  at  ordinary 
temperatures,  and  do  not  leave  a  permanent  stain  on  paper.  The 
essential  oils  are  generally  obtained  by  distilling  with  water  the 
portion  of  the  plant  in  which  they  occur.  The  essential  oil  is 
carried  over  with  the  steam,  and  separates  from  the  water  which 
is  condensed  in  the  receiver.  A  familiar  and  characteristic 
example  of  an  essential  oil  is  found  in  oil  of  cloves,  a  volatile 
liquid  of  well-known  odor. 

Exp.  115.  —  Into  a  glass  retort  of  about  250  c.  c.  capacity,  put  5 
grms.  of  whole  cloves,  and  150  c.  c.  of  water.  Insert  the  neck  of  the 
retort  loosely  into  a  receiver  or  flask,  kept  cool  as  directed  in  Exp.  9, 
§  31.  Bring  the  water  in  the  retort  to  boiling,  and  boil  until  one- 
half  of  the  liquid  has  distilled  over.  The  water  which  condenses  in 
the  receiver  will  be  rendered  turbid  by  the  "  oil  of  cloves,"  which 
has  been  carried  over  by  the  steam,  and  on  standing,  the  oil,  being 
heavier  than  water,  will  collect  in  drops  in  the  bottom  of  the  re- 


ceiver. 


Fig.  60. 


The  oil  possesses  the  characteristic 
odor  of  cloves,  which  it  also  communi- 
cates to  the  water  with  which  it  is  in 
contact.  The  water  may  be  poured 
off,  and  the  volatility  of  the  oil  illus- 
trated by  dipping  a  piece  of  filter- 
paper  into  it,  and  hanging  the  paper 
in  the  neighborhood  of  a  gas-flame. 

The  water,  which,  from  its  condensa- 
tion with  the  oil  of  cloves,  acquires 

the  same  odor,  is  an  example  of  the  fragrant  "  distilled  waters  "  of  the 

apothecaries. 


§254.]  OIL   OF  TURPENTINE.  161 

251.  Oil  of  Turpentine  (C10H16).  — When  incisions  are  made 
into  the  trunks  of  certain  species  of  pine,  there  exudes  from 
the  wounds  a  thick  resinous  substance  known  as  turpentine. 
When  ordinary  turpentine  is  distilled  with  water,  there  comes 
over,  mixed  with  the  steam,  the  vapor  of  an  oily  liquid,  which 
condenses  in  the  receiver  and  rises  to  the  top  of  the  condensed 
water.     It  is  oil  of  turpentine :  the  residue  in  the  retort  is  com- 
mon rosin. 

Exp.  116.  —  Into  a  glass  retort  of  about  250  c.  c.  capacity,  put 
40  grm*.  of  crude  turpentine,  and  200  c.  c.  of  water.  Boil  the  liquid  in 
the  retort,  and  condense  the  vapor  which  is  given  off,  as  in  Exp.  115. 
Drops  of  an  oily  liquid  will  rise  to  the  top  of  the  water  in  the  re- 
ceiver, and  form  a  layer  on  its  surface  :  it  is  oil  of  turpentine. 

In  this  experiment  the  pitch  of  northern  pines  or  of  the  spruce,  etc., 
may  be  used  instead  of  the  "  crude  turpentine." 

252.  Oil  of  turpentine  is  a  volatile  liquid,  and  may  be  dis- 
tilled unchanged.      It  will  not  mix  with  water,  but  dissolves 
freely  in  alcohol.      It  is  very  inflammable,  and  burns  with  a 
smoky  flame,  as  was  shown  in  Exp.  67,  §  181. 

Exp.  117.  —  Into  a  small  bottle  half  filled  with  water,  pour  a 
teaspoonful  of  oil  of  turpentine,  and  shake  the  bottle.  The  liquid 
is  rendered  turbid  by  the  drops  of  oil  scattered  through  it,  but  these 
drops  soon  collect  together,  forming  a  layer  on  the  top  of  the  water. 

Exp.  118.  —  Into  a  small  bottle  half  filled  with  alcohol,  pour  a 
teaspoonful  of  oil  of  turpentine,  and  shake  the  bottle.  The  oil  of 
turpentine  dissolves,  and  a  clear  homogeneous  liquid  results. 

253.  Oil  of   turpentine   is    chiefly   valuable   for   its   solvent 
powers.      It  dissolves  the  various  resins,   and  is  used  in   the 
preparation  of  varnish  :  it  also  dissolves  sulphur  and  phosphorus 
with  readiness,  and  is  one  of  the  best  solvents  of  caoutchouc. 

254.  The    essential  oils   find  .extensive   application   in   per- 
fumery :  they  are,  however,  often  replaced  by  substitutes  arti- 
ficially prepared.     Thus  for  oil  of  bitter  almonds  is  sometimes 
substituted  nitrobenzol  (§  268),  and,  as  has  already  been  stated, 
(§  233),  various  compound  ethers,  made  from  fusel  oil  and  other 
alcohols,  are  prepared  on  a  very  large  scale  for  the  confectioner 
and  perfumer. 


162  CAMPHOR.  [§  255. 

255.  Oil  of    turpentine  is    a    hydrocarbon   of   the    composition 
C10H16  :   an  isomeric   (§  240)   compound   also  occurs  in  the  various 
essential   oils,  such  as  the  oils  of  bergamot,  birch,  cloves,  caraway, 
bmons  etc.  :  most  of  them  contain,  in  addition,  a  distinctive  compound 
of  carbon,  hydrogen  and  oxygen.     Certain  of  the  essential  oils  con- 
tain sulphur  :  thus  the  essential  oils  of  garlic,  onions  and  assafoetida 
have  the  composition  (C3H.)2S.     This  compound  is  the  sulphide  of 
the  radical  allyl  (C,H5).     The  pungency  of  the  horse-radish  is  due 
to  a  sulphocyanide  of  the  same  radical. 

It  will  be  noticed  that  the  radical  allyl  has  the  same  formula  as 
that  assigned  to  glyceryl  (§  241).  It  is,  however,  merely  isomeric 
with  glyceryl,  for  the  latter  replaces  three  atoms  of  hydrogen,  i.  e.,  is 
trivalent,  while  allyl  is  univalent. 

256.  Camphor  (C10H16O). — Among  the  essential  oils,  is  classed 
ordinary  camphor.     It  is  obtained  by  distilling  with  water  the 
wood  of  a  variety  of  East  Indian  laurel.     At  ordinary  tempera- 
tures, it  is  a  white  solid,  which,  like  ice  (§  22),  volatilizes  or 
evaporates  without  first  melting  ;  it  may  readily  be  distilled,  or 
sublimed  unchanged.     Camphor  takes  fire  at  a  low  temperature 
and  burns  with  a  very  smoky  flame  ;  it  is  only  slightly  soluble 
in  water,  but  dissolves  readily  in  alcohol. 

Exp.  119.  —  Into  a  tall,  narrow  beaker  of  about  50  c.  c.  capacity 
put  2  or  3  grammes  of  camphor.  Roll  up  a  piece  of  rather  stiff  paper 
so  as  to  form  a  long  conical  cap  which  will  fit  into  the  top  of  the 
beaker.  Place  the  beaker  thus  prepared  in  a  sand-bath  and  heat  it ; 
the  camphor  soon  melts  and  begins  to  boil,  and  the  vapor  of  camphor 
is  condensed  on  the  upper  part  of  the  beaker  and  on  the  sides  of  the 
paper  cone  in  delicate,  snow-like  crystals  or  as  a  crystalline  solid. 

Exp.  120.  —  Throw  a  portion  of  the  sublimed  camphor  of  the 
preceding  experiment  into  a  dish  of  dean  water.  The  camphor  will 
slowly  dissolve  with  a  peculiar  gyratory  motion.  Throw  another 
portion  into  a  small  quantity  of  alcohol ;  the  camphor  rapidly  dis- 
solves. Place  a  third  portion  on  a  brick  and  touch  it  with  a  lighted 
match  :  the  camphor  takes  fire  and  burns  with  a  smoky  flame. 

257.  Camphor  is  a  compound  containing  oxygen  :  other  oxy- 
genated essential  oils  are  the  oil  of  bitter  almonds,  oil  of  cinna- 
mon and  oil  of  wintergreen  :  some  of  these  oils  will  be  studied 
in  the  succeeding  chapter. 


§  259.1  OLEFIAST-GAS  SERIES.  163 

The  essential  oils  which  have  just  been  studied  have  no  immedi- 
ate relation  to  the  marsh-gas  series  of  hydrocarbons,  which,  with  the 
derived  compounds,  has  formed  the  main  subject  of  this  chapter. 
They  are,  however,  conveniently  studied  in  connection  with  the  fats 
and  fixed  oils. 


CHAPTER  XVI. 

CAEBON  (continued). 

258.  In  the  series  of  hydrocarbons  known  as  the  marsh- 
gas  series,  and  described  in  the  last  chapter,  there  is  a  constant 
difference  of  CHa  in  the  formulae  of  succeeding  members  of  the 
series.     There  is  also  a  difference  of  about  30°  between  the  boil- 
ing-points of  successive  members  ;  and  other  physical  properties, 
if  studied,  would  show  a  corresponding  and  regular  increase  or 
decrease.      Such  series    are  called   homologous  series  (having 
the  same  proportion),  and  the  members  of  the  series  are  homo- 
logues  of  each  other.     For  every  such  series  a  general  algebraic 
symbol  can  be  devised  which  will  apply  to  each  member  of  the 
series.     Thus  the  general  formula  of  the  homologues  of  marsh- 
gas  is  CnH2n  4. 2 ;  if  n  =  1,  the  formula  becomes  CH4,  marsh- 
gas  ;  if  n  =  3,  the  formula  becomes  C3H8 ,  propyl  hydride,  and 
so  on. 

Another  series  of  homologous  hydrocarbons  is  that  whose  gen- 
eral formula  is  CnH2n  :  the  first  member  of  this  series  is  olefiant 
gas  (C2H4).  Members  of  this  series  occur  among  the  products 
of  the  distillation  of  various  organic  compounds,  and  also  in 
petroleum. 

259.  Olefiant  gas  or  Ethylene  (C2H4)  is  a  colorless  gas,  some- 
what soluble  in  water.     It  occurs  among  the  products  of  the  dis- 
tillation of  bituminous  coal,  but  is  best  prepared  by  the  action 
of  sulphuric  acid  on  alcohol. 


166  •      PHENYL  SERIES  OF  HYDROCARBONS,          [§  264. 

that  six  parts  by  weight  of  carbon  were  combined  with  one  part  by 
weight  of  hydrogen  ;  a  determination  of  the  specific  gravity  would 
show  the  specific  gravity  of  the  gas  referred  to  hydrogen  to  be  about 
28,  and,  as  has  been  shown  in  §  139,  the  specific  gravity  of  a  compound 
in  the  state  of  vapor  is  one-half  its  molecular  weight.  If,  then,  28 
be  multiplied  by  two,  the  result  will  be  56  for  the  weight  of  the  mole- 
cule, and  the  formula  could  not  be  C2H4,  or  C3H0 ,  or  anything,  in  short, 
except  C4H8.  Another  help  in  fixing  the  place  of  any  member  of  a 
given  series,  if  that  member  be  a  liquid  at  the  ordinary  temperature, 
is  the  determination  of  the  boiling-point  ;  for  it  has  been  found  that 
in  these  various  series  the  boiling-points  of  successive  members  in- 
crease in  a  nearly  constant  ratio. 

264.  Phenyl   Series    (CnUZTl_^.  —  If  the   liquid   and   semi- 
liquid  products  of   the  distillation  of  bituminous   coal,  which 
collectively  are  known  as  coal-tar,  be  subjected  to  distillation, 
there  will  come  off,  —  first,  a  watery  liquid  containing  ammo- 
nium salts;  next,  a  quantity  (amounting  to  from  5  to  10  per 
cent  of  the  tar  employed). of  oil  lighter  than  water,  and  techni- 
cally known  as  light-oil,  or,  when  purified,  as  coal-tar  naphtha ; 
if  the  distillation  be  carried  further,  there  will  come  off  about 
30  per  cent  of  a  heavy  oil,  called  dead  oil;  the  residue  in  the 
retort,  which  becomes  solid  on  cooling,  is  known  as  pitch  or 
artificial  asphaltum. 

The  light  oil  mentioned  above  consists  principally  of  a  mix- 
ture of  several  hydrocarbons .  of  the  general  formula  CnH  2n_6, 
known  as  the  phenyl  series.  The  members  of  this  series,  at 
present  of  most  importance  in  the  arts,  are  benzol  (C0HG)  and 
toluol  (C7H8) ;  from  these  compounds  are  derived,  by  chemical 
processes,  the  beautiful  and  varied  coloring  matters  known  as 
aniline  dyes.  While  coal-tar  is  the  chief  industrial  source  of 
the  hydrocarbons  of  the  phenyl  series,  they  have  been  obtained 
in  less  amount  from  other  sources  :  the  petroleum  from  Rangoon, 
in  the  kingdom  of  Burmah,  contains  members  of  this  series  in 
small  quantity. 

265.  Benzol  (C6H6)  at  the  ordinary  temperature  is  a  mobile, 
colorless,  volatile  liquid,  crystallizing  at  0°  :  its  vapor  is  very 
inflammable,  and  burns  with  a  smoky  flame.     The   illuminat- 


$  268  1  BENZOL  Atfb  NITRO^BESZOL.  167 

o       *  j 

ing  power  of  ordinary  coal-gas  is  probably  due  in  considerable 
measure  to  the  vapor  of  benzol  and  its  homologues.  Benzol  is 
valuable  as  a  solvent,  as  it  readily  dissolves  sulphur,  phosphorus, 
caoutchouc  and  other  substances.  Benzol  also  dissolves  wax  and 
fatty  bodies,  and  is  used  to  remove  grease-spots  from  articles  of 
silk  and  woollen. 

Exp.  121.  —  Into  a  small  bottle  containing  several  teaspoonfuls  of 
benzol,  put  a  bit  of  tallow  ;  close  the  bottle  and  shake  it :  the  fat 
is  completely  dissolved. 

Exp.  122.  —  Put  some  of  the  purest  benzol  that  can  be  obtained 
into  a  test-tube  and  immerse  the  tube  in  a  mixture  of  salt  and 
pounded  ice  or  snow  :  the  benzol  will,  if  pure,  become  solid ;  if  not 
pure  the  benzol  will  separate  from  the  rest  of  the  liquid  in  crystals, 
provided  the  percentage  of  other  bodies  (toluol,  etc. )  be  not  too  large. 

If  air  be  passed  through  benzol  or  naphtha,  it  becomes  charged 
with  inflammable  vapor,  and  may  then  be  burned  like  ordinary  coal- 
gas.  Gas-machines  constructed  on  this  principle  have  been  in  use 
for  some  years  :  latterly,  however,  benzol  and  coal-tar  naphtha,  which 
were  formerly  used  in  them,  have  been  supplanted  for  such  purposes 
by  several  cheaper  and  lighter  hydrocarbons  obtained  from  petroleum. 
The  "  benzine  "  now  sold  for  removing  grease  is  usually  not  benzol, 
but  a  mixture  of  some  of  the  most  volatile  (and  most  inflammable)  of 
the  compounds  obtained  from  petroleum. 

266.  Benzol  (C6HG)  may  be  regarded  as  the  hydride  of  a  radical, 
C6H5 ,  called  phenyl.     Benzol  would  thus  be  called  pheiiyl  hydride, 
and  the  formula  written  C6H5,H.     The  name  benzol  is  derived  from 
the  fact,  that  this  substance  can  be  obtained  by  the  distillation  under 
proper  conditions  of  benzole  acid,  —  a  substance  which  occurs  in 
nature  in  gum  benzoin. 

267.  Toluol  (C7H8)  resembles  benzol  in  its  chemical  characters, 
and  takes  part  in  similar  reactions.     It  may  be  regarded  as  methyl- 
phenyl  hydride  (C6H4(CH3),  H)  i.  e.,  phenyl  hydride,  in  which  one 
atom  of  hydrogen  has  been  replaced  by  the  radical  methyl  (CH3). 

268.  Nitrobenzol   (C6H5(NO2) ).  —  By   the  action  of  nitric 
acid  on  benzol  an  interesting  compound  known  as  nitro-benzol 
is  produced. 

Exp.  123.  —  Into  a  small  flask  put  a  teaspoonful  of  fuming  nitric 
acid.  Add  a  few  drops  of  benzol,  and  warm  the  mixture  very  gently 


168  PttODVcVlOX  OP  ANlLlNti.  [§  269. 

over  the  lamp.     Chemical  action  takes  place,  and,  upon  subsequent 
dilution  of  the  acid  mixture  with  water,  a  heavy,  oily  liquid  separates. 

Nitrobenzol  is  a  heavy,  oily  liquid  insoluble  in  water,  but 
soluble  in  alcohol  and  ether.  It  has  an  odor  resembling  that  of 
bitter  almonds,  and  is  somewhat  used  in  perfumery. 

Nitrobenzol  is  interesting,  as  affording  another  example  of  a  sub- 
stitution compound  in  which  the  group  of  atoms  NO2  takes  the  place 
of  hydrogen  (compare  nitro-glycerin,  §  245)  :  it  is,  however,  chiefly 
interesting  from  the  fact  that  it  is  one  step  in  the  process  of  making 
aniline  from  benzol. 

269.  Aniline  (C6HTN)  is  a  volatile,  oily  liquid  somewhat  solu- 
ble in  water,  and  readily  dissolved  by  alcohol  or  ether.     When 
pure,  it  is  colorless,  but  on  exposure  to  air  it  becomes  of  a  red- 
dish-brown color.     A  characteristic  reaction  of  aniline  is  afforded 
by  its  deportment  to  "  chloride  of  lime." 

Exp.  124.  —  Stir  up  a  teaspoonful  of  "  chloride  of  lime  "  (bleach- 
ing powder)  in  five  times  its  bulk  of  water,  and  filter  the  solution. 
Dissolve  a  drop  of  aniline  in  a  teaspoonful  of  water,  and  add  a 
few  drops  of  this  solution  to  a  portion  of  the  solution  of  bleaching 
powder.  A  beautiful  purple  coloration  turning  to  a  dirty  red  will 
form  in  the  liquid. 

270.  Aniline  may  be  obtained  pure  by  distilling  indigo  with 
caustic  potash  :  it  also  occurs  in  very  small  quantity  among  the 
products  of  the  distillation  of  coal,  in  the  heavy  oil  of  coal-tar 
(§  264)  ;  on  a  large  scale,  however,  it  is  made  from  nitrobenzol 
by  the  action  of  reducing  agents  (§  129).     The  formation  of 
aniline  from  nitrobenzol  may  be  illustrated  by  the  following 
experiment. 

Exp.  125.  —  Into  a  wide  test-tube  put  two  drops  of  nitrobenzol 
and  a  few  small  fragments  of  zinc.  Add  half  a  teaspoonful  of 
strong  chlorhydric  acid.  Violent  evolution  of  hydrogen  takes  place, 
and  the  nitrobenzol,  which  at  first  is  visible  in  oily  globules  at  the 
surface  of  the  effervescing  liquid,  gradually  disappears,  being  con- 
verted into  aniline,  which  dissolves  in  the  acid.  More  zinc  or  more 
acid  may  be  added  until  this  result  is  reached,  but  the  zinc  should  be 
in  excess.  When  the  nitrobenzol  has  disappeared  and  the  action  of 
the  acid  has  ceased,  dilute  a  portion  of  the  liquid  with  an  equal  bulk 


§  273.]  PROPERTIES  OF  ANlLlNE.  169 

of  water  and  add  a  drop  or  two  of  the  bleaching-powder  solution, 
used  in  Exp.  124.  The  characteristic  purple  color  produced  by  the 
action  of  bleaching  powder  upon  aniline  appears  in  the  liquid. 

The  formula  of  aniline  is  C6H7N,  and  it  may  be  regarded  as 
benzol,  in  which  one  atom  of  hydrogen  has  been  replaced  by  the 
radical  (NH2)  and  written  C6H5  ,  NH2  ;  or  it  may  be  regarded  as 
ammonia  (NH3),  in  which  one  atom  of  hydrogen  has  been  replaced 


by  phenyl  (C6H5)  and  written     H   V  N.     Compounds  of  the  ammonia 

H   ) 

type  where  a  metallic  element,  or  radical  acting  as  a  metallic  ele- 
ment, replaces  one  or  more  atoms  of  hydrogen,  are  called  amines; 
thus  aniline  would  be  called  phenyl-amine.  When  in  the  ammonia 
type  a  non-metallic  element,  or  radical  acting  as  a  non-metallic  element, 
replaces  one  or  more  atoms  of  hydrogen,  the  compound  is  sometimes 

(C2H30)} 
called  an  amide;  as  acetamide,       H        >  N,  w^here  an   atom  of 

H        ) 
hydrogen  is  replaced  by  the  hypothetical  radical  acetyl,  CJH3O. 

271.  Aniline    resembles   ammonia   in   its   conduct   towards 
acids,  uniting  directly  with  them  to  form  salts  ;  thus  with  chlor- 
hydric  acid  (HCl)  it  unites  to  form  a  compound  CGH7N,HC1,  or 
C6H8N,C1,    corresponding    to    ammonium    chloride    and    called 
"  chlorhydrate  of    aniline,"   or,  better,  phenylium  or  phenyl- 
ammonium  chloride. 

Exp.  126.  —  Pour  a  few  drops  of  aniline  into  a  porcelain  dish, 
and  hold  over  the  dish  a  rod  which  has  been  dipped  in  strong  chlor- 
hydric  acid.  White  fumes  of  phenylium  chloride  are  produced.  This 
experiment  illustrates  both  the  volatility,  and  the  basic  character  of 
aniline. 

272.  The  term  base  has  already  been  denned  in  §§  61  and  63.     In 
addition  to  the  applications  there  mentioned,  the  term  is  also  used 
to  denote  bodies  which,  like  ammonia,  NH3,  and  aniline,  C6H7N, 
contain  no  oxygen  but  unite  directly  with  acids  to  form  salts. 

273.  Aniline  Colors.  —  Aniline  itself  and  the  salts  of  aniline 
are  colorless  when  pure,  but  by  exposure  to  the  air  they  become 
more  or  less  colored.     By  the  action  of  various  chemical  agents 
on  aniline,  a  great  number  of  coloring  matters  may  be  obtained. 


170  ANILINE  COLORS.  [§  274. 

Eed,  yellow,  green,  blue  and  black,  and  that,  too,  in  very  great 
variety  and  beauty  of  shade,  are  thus  by  difference  in  the 
chemical  treatment,  all  obtained  from  the  same  raw  material ; 
namely,  coal-tar,  a  waste  product  which  formerly  was  of  very 
little  value.  The  intensity  of  some  of  these  coloring  matters  is 
very  striking. 

Exp.  127.  —  Take  a  crystal  of  aniline  red  no  larger  than  the 
Ii3ad  of  a  pin,  dissolve  it  in  a  small  quantity  of  alcohol,  and  then 
dilute  the  solution  in  a  clear  bottle  or  in  a  white  porcelain  dish  with 
a  litre  or  more  of  water.  The  red  tint  communicated  to  this  large 
quantity  of  water  will  be  very  perceptible. 

274.  The  various  so-called  aniline   dyes  are  obtained,  not 
from  the  pure  aniline,  but  from  a  mixture  of  aniline  and  tolui- 
dine.     Toluidine  is  a  body  obtained  from  toluol  (CTH8)  by  pre- 
cisely the  same  steps  as  are  taken  in  the  production  of  aniline 
from  benzol.      Pure  aniline  alone  will  not  yield  the  coloring 
matters. 

The  chemical  agents  employed  in  the  production  of  the  ani- 
line dyes  are  in  their  general  character  of  an  oxidizing  nature. 
The  effect  of  oxidation  on  the  salts  of  aniline  may  be  shown  as 
follows  :  — 

Immerse  the  poles  of  a  galvanic  battery  in  an  aqueous  solution  of 
aniline  acidulated  with  sulphuric  acid.  At  the  pole  where  oxygen  is 
evolved,  the  solution  becomes  of  a  bright  red  color.  In  Exps.  124, 
125,  the  "  chloride  of  lime  "  acted  as  an  oxidizing  agent,  although  the 
color  there  produced  has  little  permanence. 

The  various  coloring  matters  themselves  are  salts  of  several  com- 
pound bodies  which  bear  a  certain  resemblance  to  aniline,  in  that 
they  possess  a  basic  character,  that  they  may  be  regarded  as  formed 
like  aniline  on  the  ammonia  type,  and  that  they  of  themselves  are 
colorless  :  thus  the  beautiful  and  much-prized  color  known  as  'ma- 
genta is  the  salt  (chloride  or  acetate)  of  a  compound  called  rosani- 
line.  This  salt  occurs  in  commerce  finely  crystallized  ;  the  crystals 
are  of  a  brilliant  green  metallic  color  by  reflected  light,  while  by  trans- 
mitted light  they  appear  of  an  intensely  red  color. 

275.  Phenic  or  Carbolic  Acid  (C6H6O).  —  Somewhat  closely 
related  to  the  phenyl  series  of  hydrocarbons  is  a  body  which 


§277.] 


CA  RBOLIC  A  CID.  —  PICRIC  A  CID. 


occurs  in  the  oil  distilled  from  coal-tar,  and  is  known  as  phenic 
or  carbolic  acid.  The  pure  acid  crystallizes  in  colorless  needles, 
which  liquefy  in  moist  air,  and  are  sparingly  soluble  in  water. 
Phenic  acid  has  an  odor  like  wood-smoke,  and  possesses  power- 
ful antiseptic  properties.  Phenic  acid  is  used,  as  are  also  cer- 
tain of  its  salts  (phenates  or  carbolates),  to  prevent  the  spread 
of  infectious  diseases,  and  in  the  treatment  of  sores  which  give 
oifensive  discharges  :  it  is  also  used  in  the  preparation  of  a 
variety  of  "  disinfecting  "  and  "  purifying  "  powders,  and  of 
"  carbolic  acid  soap  "  used  for  similar  purposes.  The  dead  oil 
of  coal-tar,  which  is  used  as  a  preservative  of  timber,  probably 
owes  its  antiseptic  properties,  in  part  at  least,  to  the  carbolic  acid 
which  it  contains. 

Exp.  128.  —  Dissolve  1  grm.  of  crystallized  carbolic  acid  in 
100  c.  c.  of  water,  and  in  the  solution  thus  prepared  soak  a  piece  of 
fresh  meat,  or  a  small  fish,  for  one  hour,  and  then  hang  the  meat  or 
fish  up  to  dry.  The  animal  matter  thus  preserved  may  be  kept  almost 
indefinitely  in  a  dry  place  without  undergoing  putrefaction. 

Carbolic  acid  may  be  regarded  as  the  hydrate  of  the  radical  phei>yl, 
and  written  C6H5,  HO.  It  evidently  bears  the  same  relation  to 
phenyl  that  the  alcohols  do  to  the  radicals  of  the  marsh-gas  series  ;  it 
differs,  however,  from  the  alcohols  in  important  respects,  and  is  one 
of  a  class  of  similar  compounds  called  phenols. 

276.  The   dead    oil   of   coal-tar  contains  several  other   acid 
bodies  analogous  to  carbolic  acid  :  it  also  contains  several  bases, 
among  which  is  aniline  (§  270),  and  several  hydrocarbons,  among 
which  may  be  mentioned  naphthalin  (§  279),  and  anthracene 
(§  281). 

277.  Trinitrophenic  or  Picric  Acid.  —  When  phenic  acid  is 
treated  with  strong  nitric  acid,  a  compound  known  as  picric  acid 
is  produced.     It  is  a  substance  which  forms  yellow  crystals  not 
very  soluble  in  water,  but  possessing  great  coloring  power.     It  is 
readily  soluble  in  alcohol  and  ether,  and  is  used  principally  in 
dyeing  silk.     Picric  acid  may  be  formed  by  the  action  of  nitric 
acid  on  various  other  organic  compounds,  especially  on  certain 
gum  resins  ;  on  the  large  scale,  however,  it  is  manufactured  from 
phenic  or  carbolic  acid. 


172  PICRIC  ACID.-XAPHTHALIX.  [$  278. 

Exp.  129. —  Into  a  flask  of  150  c.  c.  capacity,  put  two  teaspoon- 
i'uls  of  fuming  nitric  acid.  Add  cautiously  and  very  gradually,  half 
a  teaspoonful  of  crystallized  carbolic  acid  or  of  the  liquefied  crystals. 
The  action  which  takes  place  is  very  violent,  and  nitrous  fumes  are 
copiously  disengaged.  When  the  action  has  subsided  allow  the  flask 
to  become  cold  ;  yellow  crystals  of  picric  acid  will  be  found  in  the 
liquid. 

This  experiment  should  be  performed  where  there  is  a  good 
draught  of  air,  and  the  flask  should  be  held  at  arms'  length  on  each 
successive  addition  of  carbolic  acid. 

Exp.  130. —  Dissolve  1  grm.  of  crystallized  picric  acid,  in  125  c.  c. 
of  water.  Preserve  one-half  the  solution  for  use  in  a  subsequent  ex- 
periment ;  warm  the  remainder  gently,  and  immerse  in  it  some 
woollen  material,  —  a  skein  of  white  yarn,  or  piece  of  white  flannel. 
After  a  few  minutes,  remove  the  wool,  and  rinse  it  in  water  :  it  will 
be  dyed  a  brilliant  yellow. 

The  formula  of  picric  acid  is  C6H3(NO2)3O,  or  phenic  acid, 
C6H6O,  in  which  three  atoms  of  hydrogen  are  replaced  by  three 
atoms  of  the  radical  NO2  ;  hence  the  chemical  name,  tri-nitro- 
plienic  acid. 

278.  Picric    acid  is  used  in  the  preparation  of   potassium 
picrate,  which  is  an  ingredient  of  certain  substitutes  for  gun- 
powder.      The   picrates    are    yellow  crystalline   salts.      When 
heated,  they  are  decomposed  with  explosion  :  picric  acid  itself 
explodes  if  heated  suddenly,  although  with  care  it  can  be  grad^ 
ually  sublimed.     Potassium  picrate  will  explode,  if  struck  with 
a  hammer. 

279.  Naphthalin   (C10H8).  —  This   hydrocarbon  is  an  abun- 
dant product  of  the  distillation  of  coal-tar,  occurring  especially 
in  the  dead  oil,  and  in  largest  amount  towards  the  last  part  of 
the  distillation.     It  is  solid  at   ordinary  temperatures,  and   is 
separated  from  the  accompanying  liquid  products  by  pressure. 
It  is  insoluble  in  water,  but  dissolves  in  alcohol,  and  may  be 
purified  by  recrystallization  from  this  solvent.     It  can  also  be 
sublimed  unchanged.     It  forms  white  pearly  crystals  greasy  to 
the  touch  :  it   is  not  readily  inflammable,   but,  when  lighted, 
burns  with  a  smoky  flame. 

280.  Naphthalin  enters  into  direct  combination  with  chlorine  and 


§  282.]  DISTILLATION  OF  WOOD.  173 

bromine  in  different  proportions  :  it  also  forms,  with  these  elements, 
a  great  number  of  substitution  compounds,  as  they  are  called. 
These  compounds  preserve  the  type  of  naphthalin,  but  in  them  one 
or  more  atoms  of  chlorine  or  bromine,  or  both  these  elements,  take 
the  place  of  the  same  number  of  atoms  of  hydrogen.  One  of  these 
compounds  furnishes  a  good  example  of  isomerism,  defined  in 
§  240.  Of  the  compound  whose  formula  is  C^HyClg,  there  have 
been  recognized  .seven  'distinct  varieties  ;  that  is,  there  are  seven 
compounds  which  have  identically  the  same  percentage  composition, 
and  to  each  of  which  the  formula  C10HGC12  will  apply,  but  which 
differ  from  each  other  in  respect  to  solubility,  fusing  point  and  be- 
havior to  chemical  agents.  These  differences  may  be  imagined  to  be 
due  to  diversities  in  the  arrangement  of  the  atoms  in  the  several 
compounds. 

281.  Anthracene    (C14H10)    is  a  white   solid,   which   accom- 
panies naphthalin  in  the  last  products  of  the  distillation  of  coal- 
tar.      It   is  insoluble   in  alcohol,   and  may  be   separated  from 
naphthalin  by  treating  the  mixture  of  these  two  substances  with 
this  solvent,  which  removes  the  naphthalin.     It  is  interesting 
chiefly  because  alizarin,  the  coloring  matter  of  the  madder-root, 
has  recently  been  made  from  it. 

282.  Destructive  Distillation  of  Wood.  —  In  the  distilla- 
tion of  wood,  as  in  that   of  coal,  the   nature  of  the  products 
varies  somewhat  according  to  the  temperature  employed.     The 
gas  obtained  consists  mainly  of  carbon  protoxide,  carbonic  acid, 
marsh-gas  and  hydrogen  ;    of  the   liquid  and  semi-liquid  pro- 
ducts, a  portion  is  insoluble  in  water  and  is  composed  of  various 
hydrocarbons,   some  of  which  have  already  been  studied.     Of 
the  portion  soluble  in  water,  the  most  important  constituents 
are  wood-spirit   (methyl  alcohol,  §  230),  methyl  acetate  and 
acetic  or  pyroligneous  acid  (§  238). 

The  greatest  yield  of  acetic  acid  is  obtained  by  distilling  the 
wood  at  low  temperatures.  The  liquid  portion,  insoluble  in 
water,  contains  among  other  bodies,  some  of  the  homologues 
of  benzol,  and  a  body  called  kreasote,  which,  when  pure,  is  a 
colorless  liquid  of  pungent  taste  and  smoky  odor.  The  peculiar 
odor  of  wood-smoke  is  owing  to  the  presence  of  this  bodv, 
15* 


174  OIL   OF  BITTER  ALMONDS.  [§  283. 

Kreasote  possesses  very  powerful  antiseptic  properties  :  meat 
and  fish  may  be  preserved  from  putrefaction  by  immersion  in  a 
very  dilute  solution  of  kreasote,  or  by  exposure  to  wood-smoke. 
Much  of  what  is  now  sold  as  kreasote  is  actually  carbolic  acid, 
which,  as  has  been  seen  in  Exp.  128,  possesses  marked  antisep- 
tic properties. 

Paraffin  (C27H56?)  is  also  among  the  products  of  the  distilla- 
tion of  wood  ;  but  the  paraffin  of  commerce  is  now  obtained 
almost  entirely  from  petroleum. 

In  §  257,  among  the  essential  oils,  was  mentioned  the  oil  of 
bitter  almonds.  This  substance  is  closely  allied  with  the  phenyl 
series  of  hydrocarbons,  and  may  be  most  conveniently  studied 
at  this  point. 

283.  Oil  of  Bitter  Almonds,  —  If  the  kernels  of  the  bitter 
almond  be  crushed,  there  is  expressed  a  nearly  colorless  fixed  oil 
without  taste  or  odor,  and  identical  with  that  obtained  from  the 
sweet  almond.     If,  however,  the  crushed  kernels  are  moistened 
with  water,  the  familiar  odor  of  bitter  almonds  is  soon  devel- 
oped.    Bitter  almonds  contain  a  peculiar  nitrogenous  substance, 
amygdalin  (C20H27NOn ,  3  H2O) ;  under  the  influence  of  another 
nitrogenous  body,  contained  in  the  kernels  and  resembling  some- 
what the  diastase  of  malt  (§  300),  the  amygdalin  is  converted 
into   an   essential   oil,   the   essence  or  oil  of  bitter  almonds. 
There  is  formed  at  the  same  time  a  quantity  of  cyanhydric  acid 
(§  212),  which  accompanies  the  essence  when  it  is  distilled,  and 
communicates  to  it  its  highly  poisonous  qualities.     The  purified 
oil  is  not  poisonous. 

284.  The  formula  of  the  oil  of  bitter  almonds  is  C7HGO,  and  it 
may  be  regarded  as  a  hydride  of  a  hypothetical  radical  benzoyl 
(C7H5O).     The  relation  of  the  oil  of  bitter  almonds  to  the  phenyl 
series  (§  264)  is  seen  by  regarding  it  as  an  aldehyde  bearing  the 
same  relation  to  toluol,  C.H8,  (§  267),  that  ordinary  aldehyde  (§  235) 
dees   to   ethyl   hydride,   C2H6.      It   behaves   like   an   aldehyde  :    in 
contact  with  the  air,  it  oxidizes  to  benzole  acid  (C.HGO2),  which, 
to  carry  out  the  same  comparison,  answers  to  acetic   acid.      There 
is  also  a  compound  which  corresponds  to  alcohol,  benzyl  alcohol 
(C7H,0). 


BEN  ZOIC  ACID.  -ACETYLENE.  175 

The  relations  of  these  compounds  to  each  other  are  shown  in  the 
following  table  :  — 

Radical.  —  Ethyl.  Ether.  —  Ethyl  ether. 


Methyl-phenyl  or  benzyl.  Benzyl  ether. 

C7H7  (C7Hr)20 

Hydride.  —  Ethyl  hydride.  Aldehyde.  —  Acetic  aldehyde. 

(C2H5)H  C2H30,H 

Toluol  or  benzyl  hydride.  Bitter  almond  oil. 

C7H7,H  C7H50,H 

Alcohol.  —  Ethyl  alcohol.  Acid.  -  Acetic  acid. 

C2H.,HO  C2H30,HO 

Benzyl  alcohol.  Benzoic  acid. 

C7H_,HO  C7H50,HO 

285.  Benzoic  acid  (C7H6O2)  occurs  in  many  balsams,  being  found 
most  abundantly  in  gum  benzoin,  a  sort  of  balsam  containing  besides 
benzoic  acid   several  resins.     It  may  be  prepared   artificially  from 
bitter  almonds,  as  has  been   stated  ;    it  may  also  be  prepared  by 
oxidizing  naphthalin  with  nitric  acid,  and  heating  the  product  with 
slaked  lime.     Calcium  benzoate  is  thus  produced,  from  which  benzoic 
acid  may  be  set  free.     Benzoic  acid  is  a  white  crystalline  solid,  of 
pearly  lustre. 

If  benzoic  acid  be  distilled  with  excess  of  lime,  benzol  is  produced 
in  accordance  with  the  equation  :  — 

CaO  +  C7H602  =  C6H6  -f  CaCO3. 

Lime.  Benzoic  Benzol.  Calcium 

acid.  carbonate. 

286.  The  Acetylene  Series  (cnH2n_2).  —  Acetylene  (c2H2) 
is  a  transparent,  colorless  gas,  which  occurs  in  small  quantities 
in  illuminating  gas.     It  may  be  formed  by  the  direct  union  of 
carbon  and  hydrogen  at  very  high    temperatures.      It  is    also 
formed  during  the  incomplete   combustion  of  other  hydrocar- 
bons.    The  peculiar  odor  noticed  when  the  gas  in  a  Bunsen  lamr 
burns  at  the  lower  opening  is  due  to  the  formation  of  acetylene. 
Acetylene  burns  with  a  bright  flame,  and  as  it  is  present  to  some 
extent  in  coal-gas,  it  doubtless  contributes  to  the  illuminating 
effect  of  the  gas. 


176  MANUFACTURE  OF  SUGAR.  [§  287. 

CHAPTER  XVII. 

CARBON  (continued). 

287.  In   this    chapter  several  of  the    natural   organic    com- 
pounds will  be  considered  which  play  a  part  in  the  life  and 
growth  of  plants  and  animals,  or  are  the  direct  product  of  such 
growth.     A  great  number  of  different  compounds  occur  in  the 
vegetable  kingdom,  some  being  found  only  in  particular  species 
of  plants,  or  even  being  confined  to  single  portions  of  particular 
plants,  while  others  occur  almost  universally  in  nearly  all  vege- 
table organisms.     Among  these  substances  which  occur  so  widely 
diffused  are  water,  which  sometimes   amounts  to  90  per  cent 
of  the  green  plant,  woody  fibre  or  cellulose,  gum,  starch  and 
sugar.      The  last-named  compound  will  first  claim   our  atten- 
tion. 

The  class  of  bodies  known  as  sugars  contains  several  varieties, 
of  which  the  most  familiar  is  ordinary  cane-sugar. 

288.  Cane-Sugar  or  Sucrose  (C12H22On)  occurs  in  the  juice 
of  various  plants,   notably  in  that  of  the  sugar-cane,  beet-root, 
sugar-maple    and    certain    varieties    of   palm.     In    this  country 
sugar  made  from  the   cane  is  used  almost  exclusively,  but  on 
the  continent  of  Europe  large  quantities  are  made  from  the  beet- 
root. 

289.  Sugar  Manufacture. — In  the   manufacture  of  cane-sugar, 
the  juice    is   extracted   from    the    canes   by   passing   them   between 
grooved  iron  cylinders.     The  liquid  thus  extracted  contains  not  only 
sugar  in  solution,  but  also  certain  albuminous  and  waxy  matters,  and 
has  a  great  tendency  to  ferment.     It  is  therefore  immediately  treated 
with  a  small  proportion  of  milk  of  lime  and  heated  for  a  short  time. 
The  lime  serves  to  correct  any  acidity  and  at  the  same  time  enters 
into  combination  with  some  of  the  impurities  of  the  juice  ;  the  albu- 
minous matters,  coagulated  by  the  heat,  entangle  these  impurities  and 
rise  with  them  as  a  thick  scum  to  the  surface  of  the  liquid.     The 
scum  is  removed,  and  the  clear  liquid  is  evaporated  in  open  pans  until 
of  such  a  consistency  that  on  cooling  crystals  of  sugar  separate.     The 


§  289.1  MANUFACTURE  OF  SUGAR.  177 

crystals,  after  draining,  form  what  is  known  as  brown  sugar  ;   the 
mother-liquor  which  drains  off  is  molasses. 

Until  recently  almost  all  the  sugar  manufactured  was  exported 
from  the  place  of  its  production  as  "  brown  "  or  "  muscovado  "  sugar, 
and  was  subsequently  refined  in  England  or  in  the  more  Northern 
cities  of  the  United  States.  The  refining  -consists  in  dissolving  the 
sugar  in  water,  removing  the  impurities  and  coloring  matters  by  filter- 
ing the  liquor,  and  passing  it  through  layers  of  animal  charcoal,  and 
then  evaporating  and  crystallizing.  The  evaporation  is  conducted  in 
<a  peculiar  manner.  If  a  solution  containing  a  certain  amount  of 
common  salt  be  evaporated,  the  salt  is  recovered  unchanged,  no  mat- 
ter how  rapidly  or  how  slowly  the  evaporation  takes  place  ;  this  is 
not  the  case  with  sugar.  If  a  solution  of  cane-sugar  be  boiled,  a 
certain  amount  of  the  sugar  undergoes  a  change  :  it  is  converted  into 
another  variety  of  sugar,  or  rather  a  mixture  of  two  varieties  of  sugar. 
These  varieties  of  sugar  (which  will  be  considered  hereafter)  do  not 
crystallize  out  with  the  cane-sugar,  but  form  the  main  part  of  the 
sirup  which  drains  off  from  the  crystals.  The  amount  of  sugar  which 
is  thus  changed  depends  among  other  things  upon  the  length  of  time 
during  which  the  solution  is  boiled,  and  also  upon  the  temperature 
employed.  By  boiling  in  open  pans,  much  sugar  is  thus  lost ;  and  in 
the  sugar  refineries  the  sugar  is  therefore  boiled  in  enormous  closed 
iron  or  copper  kettles,  from  which  the  air  can  be  exhausted.  Under 
these  circumstances  the  sugar  solution  boils  at  a  much  lower  tempera- 
ture than  it  would  in  the  open  air,  and  all  risk  of  burning  is  avoided. 
When  a  sufficient  degree  of  concentration  is  reached,  the  liquor  is 
removed  from  the  "  vacuum-pan,"  as  the  kettle  is  called,  and  allowed 
to  crystallize.  The  crystals  are  dried  either  by  allowing  them 
to  drain  in  moulds  (loaf-sugar),  or  by  forcing  the  mother-liquor  out 
by  means  of  a  centrifugal  machine  (granulated  sugar).  When,  by 
further  concentration  of  the  liquor  which  drains  off,  and  by  repeated 
crystallizations,  the  greater  part  of  the  sugar  has  been  obtained, 
the  mother-liquor  remaining  from  the  last  crop  of  crystals  is  sold 
as  sirup.  Until  within  a  few  years,  almost  all  the  refining  of  sugar 
was  done  in  England  and  the  Northern  United  States,  and  enormous 
quantities  of  sugar  are  still  refined  in  these  countries  ;  of  late  years, 
however,  vacuum-pans  and  other  improved  apparatus  have  been  intro- 
duced into  the  places  where  sugar  is  produced,  and  very  good  white 
sugar  is  there  made  directly  from  the  juice  of  the  cane.  The  follow- 
ing experiment  will  illustrate  the  principle  of  the  vacuum-pan  alluded 
to  above. 


178  VARIETIES  OF  CANE-SUGAR.  [§  290. 

Exp.  131.  —  Fill  a  round-bottomed  flask  of  500  c.  c.  capacity  half 
full  of  water,  and  boil  it  over  the  lamp.  When  the  boiling  has  con- 
tinued for  some  time,  and  the  air  in  the  upper  part  of  the  flask  has 
been  expelled  by  the  steam,  remove  the  lamp,  grasp  the  neck  of  the 
flask  with  a  dry  warm  towel  and  immediately  insert  a  tightly  fitting 
cork.  Support  the  flask  in  an  inverted  position  and  pour  cold  water 
over  the  bottom,  which  is  now  uppermost,  so  as  to  condense  the 
steam  ;  there  will  be  formed  a  vacuum  above  the  water  and  boiling  will 
recommence.  This  may  be  repeated  several  times,  until  the  water 
has  cooled  down  to  a  considerable  extent. 

290.  The  process  of  the  manufacture  of  sugar  from  the  beet 
is    very    similar    to    that    already    described.     A  comparatively 
small  quantity  of  sugar  is  made  in  the  Northern  United  States 
by  concentrating  the   sap  of  the  sugar-maple,  and  in  the  East 
quite  considerable  quantities  are  made  from  the  juice  of  several 
varieties  of  palm,  especially  the  date-palm. 

The  sugar  obtained  from  all  these  sources  is  identical  with 
that  obtained  from  the  sugar-cane.  Care  is,  however,  required 
in  the  purification  in  order  to  remove  completely  a  peculiar  taste 
which  betrays  the  origin  of  the  sugar.  Maple-sugar  and  palm- 
sugar  are  sold  in  the  crude  state,  the  peculiar  taste  being  agree- 
able to  many  persons ;  beet-sugar  is  always  refined,  as  the  taste 
of  the  crude  article  is  offensive  to  every  one. 

Exp.  132.  —  Stop  the  neck  of  a  funnel  loosely  with  a  bit  of 
pumice-stone  and  fill  it  nearly  to  the  top  with  common  maple-sugar, 
which  has  been  reduced  to  a  rather  fine  powder.  Prepare  a  saturated 
solution  of  sugar  by  dissolving  50  grms.  of  white  sugar  in  20  c.  c.  of 
hot  water,  and  allowing  the  solution  to  cool.  Pour  some  of  this  solu- 
tion upon  the  maple-sugar  as  it  lies  in  the  funnel,  so  as  to  make  a 
layer  0.5  c.  m.  thick  :  support  the  funnel  in  a  small  bottle,  cover  it 
with  a  sheet  of  paper,  and  let  it  remain  for  some  time.  The  solution 
of  sugar  will  gradually  work  its  way  through  the  maple-sugar,  and 
being  already  saturated,  it  will  not  dissolve  any  of  it  ;  it  will,  how- 
ever, carry  with  it  a  considerable  quantity  of  the  coloring  matter  and 
when  the  maple-sugar  has  drained,  it  will  be  much  lighter  colored 
than  before,  and  will  have  lost,  to  a  certain  degree,  its  peculiar  taste. 

291,  Sucrose  is  readily  soluble  in  water,  and  may  be  ob- 


§  294.1  DEXTROSE  AND  LEW  LOSE.  179 

tained  from  its  solution  in  large  transparent  crystals,  rock- 
candy.  Sucrose  melts  at  160°  to  a  colorless  liquid,  which  on 
cooling  forms  a  transparent  amber-colored  mass,  barley-sugar. 
When  sucrose  is  heated  to  215°,  water -is  given  off,  and  a  brown 
mass,  caramel,  remains. 

Bxp.  133.  —  Heat  cautiously  a  small  quantity  of  white  sugar  in  a 
porcelain  dish  until  it  melts.  Allow  the  pasty  liquid  to  cool  rap- 
idly ;  the  product  is  barley-sugar.  Heat  "again  to  a  still  higher, 
but  not  too  high  temperature  ;  the  sugar  turns  brown,  froths,  gives 
off  pungent  vapors  and  there  remains  a  dark"  brown  mass,  which  is 
caramel.  This  substance  is  soluble  in  water,  and  is  "used  to  color 
soups,  ale,  wines  and  so  forth.  If  sugar  be  heated  rapidly  and  rather 
strongly,  it  will  take  fire  and  burn,  leaving  "a  black  carbonaceous 
residue. 

292.  When  a  solution  of  sucrose  is  subjected  to  the.  action  of  yeast, 
the  sucrose  is  converted  into  two  isqmeric  (see  §240)  varieties  of 
sugar,  dextrose  and  levulose,  in  accordance  with  the. equation  : 


•CM*,On  +  H20  =  C6H1208 :+  C6H120, 

Sucrose.  Dextrose.  .    •  .  Levulose. ......     

.The  same  change  may  be  effected  by. simply  boiling  the  solution. of 
sucrose  for  a  .long  time  ;  it  may  be  effected  more  rapidly  by  the  ad- 
dition of  a  small  amount  of  almost  any  organic  acid  or  of  .one  of  the 
stronger,  acids,  such,  as  sulphuric  or  chlorhydric.  These  facts  have  a 
practical  bearing  on  the  manufacture  of  sugar  ;  for,  as  has  been  already 
stated,  a  considerable  amount  of  cane-sugar  is  lost,  even  in  the  best- 
conducted  processes  of  extracting  it  from  the  juice  and  refining  the 
crude  product. 

293.  The  most  striking  physical  property  of  sugar  is  its  action 
upon  polarized  light.     If  a  beam  of  polarized  light  be  passed  through 
a  solution  of  cane-sugar,  the  plane  of  polarization  will  be  rotated 
towards  the  right :  the  same  is  true  of  dextrose,  though  in  a  less 
degree,  and  hence  its  name  (Latin,  dextra,  the  right  hand)  ;  levulose, 
on  the  contrary,  turns  the  plane  of  polarization  to  the  left  (Latin, 
lava,  the  left  hand).     The  amount  of  rotation  in  any  case  depends 
upon  the  amount  of  sugar  in  the  solution  examined,  and  upon  this 
fact  methods  have  been  based  for  the  quantitative  estimation  of  cane- 
sugar  in  sirups  or  solution  thereof. 

294.  Dextrose,  Grape-  or  Starch-Sugar  (C6H12O6),  also  called 
Glucose,  occurs  together  with  sucrose  and  levulose  in  many"  ripe 


180  DEXTROSE  AND  LEVULOSE.  [§  295. 

fruits,  such  as  apricots,  peaches,  pineapples  and  strawberries  ; 
together  with  levulose  it  occurs  in  honey  and  in  certain  fruits, 
among  which  are  grapes,  cherries  and  gooseberries.  The  sugar 
formed  in  dried  fruits,  such  as  raisins,  which  have  candied,  is 
grape-sugar.  It  may  also  be  prepared  by  boiling  starch  in  water 
acidulated  with  sulphuric  acid. 

Exp.  134.  —  Into  a  flask  of  250  c.  c.  capacity,  introduce  100  c.  c. 
of  water.  Add  1  c.  c.  of  strong  sulphuric  acid,  and  heat  the  mixture 
to  boiling.  In  a  porcelain  mortar,  rub  10  grms.  of  starch  with  enough 
water  to  make  a  cream,  and  pour  the  mixture,  little  by  little,  into  the 
boiling  liquid,  taking  care  not  to  interrupt  the  boiling.  The  starch 
dissolves  without  forming  a  paste.  Boil  for  three  or  four  hours,  re- 
placing from  time  to  time  the  water  lost  by  evaporation,  and  then  add 
powdered  chalk  (calcium  carbonate)  until  the  liquid  is  no  longer  acid. 
"When  the  mixture  has  become  cold,  filter  off  the  insoluble  calcium 
sulphate  formed  by  the  action  of  the  sulphuric  acid  on  the  calcium 
carbonate,  and  evaporate  the  solution  at  a  gentle  heat  to  a  sirupy 
consistency.  The  solution  contains  dextrose,  which  on  long  standing 
may  separate  from  the  liquid  in  crystals. 

Dextrose  may  be  obtained  from  cellulose  or  woody  fibre  (§  309), 
by  treating  linen  or  cotton  shreds,  or  even  sawdust,  with  strong  sul- 
phuric acid.  The  mixture  is  allowed  to  stand  for  24  hours,  and  then 
diluted  with  a  large  quantity  of  water  and  boiled.  The  acid  is  sub- 
sequently neutralized  with  chalk,  and  the  dextrose  obtained,  as  in 
Exp.  134.  In  these  experiments,  the  sulphuric  acid  acts  in  some  un- 
explained manner  by  its  simple  presence.  When  the  reaction  is 
completed,  there  remains  in  the  solution  the  same  amount  of  sulphuric 
acid  as  was  added  in  the  beginning  of  the  experiment. 

295.  Dextrose  may  be  obtained   in  crystals  which  contain 
one  or  two  equivalents  of  water ;  it  usually  occurs,  however, 
in  the  state  of  a  thick  solution,  as  in  Exp,  134,  or  as  it  exists 
in  sirup.     It  is  used  in  the  manufacture  of  alcohol  (§  226), 
in  the  sweetening  of  certain  varieties  of  wine  and  beer,  and  is 
sometimes  employed  to  adulterate  cane  or  beet  sugar,  especially 
in  confectionery.     It  possesses  less  sweetening  power  than  cane- 
sugar. 

296.  Levulose  or  Fruit-Sugar  (C,HUO9)  occurs  mixed  with 


§  300.  ]  LA  CTOSE.  —  FERMENT  A  TION.  \  8 1 

one  or  both  of  the  preceding  varieties  of  sugar,  in  honey 
and  in  many  kinds  of  fruits.  It  is  formed  together  with  dex- 
trose, when  ordinary  sugar  is  boiled,  and  hence  occurs  in  mo- 
lasses. It  may  be  made  from  inulin,  a  variety  of  starch  ob- 
tained from  the  dahlia  and  some  other  .plants,  in  the  same  way 
in  which  dextrose  was  made  from  common  starch  (Exp.  134, 
§  294).  It  does  not  crystallize  :  by  evaporating  its  solution,  it 
is  obtained  as  a  colorless,  amorphous  mass. 

297.  Under  the  influence  of  yeast,  both  dextrose  and  levulose  un- 
dergo fermentation,*  carbonic  acid  and  alcohol  being  formed.     Cane- 
sugar  does  not  undergo  fermentation  directly,  but  is  first  changed 
into  a  mixture  of  dextrose  and  levulose. 

298.  A  characterististic   test  for  dextrose   and   levulose   is 
afforded  by  their  chemical  action  on  an  alkaline  solution  of  a 
salt  of  copper. 

Exp.  135.  —  To  a  dilute  solution  of  copper  sulphate,  add  enough 
caustic  potash  solution  to  dissolve  the  precipitate  which  forms  at 
first.  To  a  portion  of  the  solution  thus  prepared,  add  a  few  drops  of 
a  solution  of  white  sugar,  and  warm  the  mixture  :  no  change  takes 
place.  To  another  portion  add  a  solution  of  grape-sugar,  and  warm 
the  mixture  :  a  yellowish  precipitate  of  a  hydrate  of  copper  forms  in 
the  liquid,  and  by  the  boiling  is  converted  into  the  red  copper  sub- 
oxide.  By  means  of  this  test,  the  presence  of  dextrose  and  levulose 
may  be  shown  in  molasses  or  sirup. 

299.  Lactose  or  Milk-Sugar  (C12H22O11)  is  an  animal  product, 
nearly  related  to  cane-sugar.     It  is  less  sweet  and  less  soluble  in 
water  than  cane-sugar.     It  occurs  in  the  milk  of  the  mammalia, 
and  is  obtained,  chiefly  in  Switzerland,  by  evaporating  the  whey 
of  cows'  milk  :  it  crystallizes  in  hard,  gritty  crystals,  which  con- 
tain one  molecule  of  water  of  crystallization. 

300.  Fermentation.  —  As  has  already  been  stated  in  §  225, 
and  illustrated  by  Exp.  100,  §  226,  the  juice  of  various  fruits, 
or  aqueous  solutions  of  grape-sugar,  in  the  presence  of  an  organ- 
ized substance  known  as  yeast,  undergo  a  change.     The  sugar 
is  gradually  converted  into  alcohol,  while  carbonic  acid  escapes 
from  the  liquid.     Cane-sugar,  as  such,   does  not  undergo  this 

16 


180  DEXTROSE  AND  LEVULOSE.  [§  295. 

fruits,  such  as  apricots,  peaches,  pineapples  and  strawberries  ; 
together  with  levulose  it  occurs  in  honey  and  in  certain  fruits, 
among  which  are  grapes,  cherries  and  gooseberries.  The  sugar 
formed  in  dried  fruits,  such  as  raisins,  which  have  candied,  is 
grape-sugar.  It  may  also  be  prepared  by  boiling  starch  in  water 
acidulated  with  sulphuric  acid. 

Exp.  134.  —  Into  a  flask  of  250  c.  c.  capacity,  introduce  100  c.  c. 
of  water.  Add  1  c.  c.  of  strong  sulphuric  acid,  and  heat  the  mixture 
to  boiling.  In  a  porcelain  mortar,  rub  10  grins,  of  starch  with  enough 
water  to  make  a  cream,  and  pour  the  mixture,  little  by  little,  into  the 
boiling  liquid,  taking  care  not  to  interrupt  the  boiling.  The  starch 
dissolves  without  forming  a  paste.  Boil  for  three  or  four  hours,  re- 
placing from  time  to  time  the  water  lost  by  evaporation,  and  then  add 
powdered  chalk  (calcium  carbonate)  until  the  liquid  is  no  longer  acid. 
When  the  mixture  has  become  cold,  filter  off  the  insoluble  calcium 
sulphate  formed  by  the  action  of  the  sulphuric  acid  on  the  calcium 
carbonate,  and  evaporate  the  solution  at  a  gentle  heat  to  a  sirupy 
consistency.  The  solution  contains  dextrose,  which  on  long  standing 
may  separate  from  the  liquid  in  crystals. 

Dextrose  may  be  obtained  from  cellulose  or  woody  fibre  (§  309), 
by  treating  linen  or  cotton  shreds,  or  even  sawdust,  with  strong  sul- 
phuric acid.  The  mixture  is  allowed  to  stand  for  24  hours,  and  then 
diluted  with  a  large  quantity  of  water  and  boiled.  The  acid  is  sub- 
sequently neutralized  with  chalk,  and  the  dextrose  obtained,  as  in 
Exp.  134.  In  these  experiments,  the  sulphuric  acid  acts  in  some  un- 
explained manner  by  its  simple  presence.  "When  the  reaction  is 
completed,  there  remains  in  the  solution  the  same  amount  of  sulphuric 
acid  as  was  added  in  the  beginning  of  the  experiment. 

295.  Dextrose  may  be  obtained   in  crystals  which  contain 
one  or  two  equivalents  of  water ;  it  usually  occurs,  however, 
in  the  state  of  a  thick  solution,  as  in  Exp,  134,  or  as  it  exists 
in  sirup.     It  is  used  in  the  manufacture  of  alcohol  (§  226), 
in  the  sweetening  of  certain  varieties  of  wine  and  beer,  and  is 
sometimes  employed  to  adulterate  cane  or  beet  sugar,  especially 
in  confectionery.     It  possesses  less  sweetening  power  than  cane- 
sugar. 

296.  Levulose  or  Fruit-Sugar  (cfHuOe)  occurs  mixed  with 


§  300.  ]  LA  CTOSE.  —  FERMENT  A  TION.  181 

one  or  both  of  the  preceding  varieties  of  sugar,  in  honey 
and  in  many  kinds  of  fruits.  It  is  formed  together  with  dex- 
trose, when  ordinary  sugar  is  boiled,  and  hence  occurs  in  mo- 
lasses. It  may  be  made  from  inulin,  a  variety  of  starch  ob- 
tained from  the  dahlia  and  some  other  .plants,  in  the  same  way 
in  which  dextrose  was  made  from  common  starch  (Exp.  134, 
§  294).  It  does  not  crystallize  :  by  evaporating  its  solution,  it 
is  obtained  as  a  colorless,  amorphous  mass. 

297.  Under  the  influence  of  yeast,  both  dextrose  and  levulose  un- 
dergo fermentation,-  carbonic  acid  and  alcohol  being  formed.     Cane- 
sugar  does  not  undergo  fermentation  directly,  but  is  first  changed 
into  a  mixture  of  dextrose  and  levulose. 

298.  A  characterististic   test  for  dextrose    and   levulose   is 
afforded  by  their  chemical  action  on  an  alkaline  solution  of  a 
salt  of  copper. 

Exp.  135.  —  To  a  dilute  solution  of  copper  sulphate,  add  enough 
caustic  potash  solution  to  dissolve  the  precipitate  which  forms  at 
first.  To  a  portion  of  the  solution  thus  prepared,  add  a  few  drops  of 
a  solution  of  white  sugar,  and  warm  the  mixture  :  no  change  takes 
place.  To  another  portion  add  a  solution  of  grape-sugar,  and  warm 
the  mixture  :  a  yellowish  precipitate  of  a  hydrate  of  copper  forms  in 
the  liquid,  and  by  the  boiling  is  converted  into  the  red  copper'  sub- 
oxide.  By  means  of  this  test,  the  presence  of  dextrose  and  levulose 
may  be  shown  in  molasses  or  sirup. 

299.  Lactose  or  Milk-Sugar  (C13H28OU)  is  an  animal  product, 
nearly  related  to  cane-sugar.     It  is  less  sweet  and  less  soluble  in 
water  than  cane-sugar.     It  occurs  in  the  milk  of  the  mammalia, 
and  is  obtained,  chiefly  in  Switzerland,  by  evaporating  the  whey 
of  cows'  milk  :  it  crystallizes  in  hard,  gritty  crystals,  which  con- 
tain one  molecule  of  water  of  crystallization. 

»  300.  Fermentation.  —  As  has  already  been  stated  in  §  225, 
and  illustrated  by  Exp.  100,  §  226,  the  juice  of  various  fruits, 
or  aqueous  solutions  of  grape-sugar,  in  the  presence  of  an  organ- 
ized substance  known  as  yeast,  undergo  a  change.  The  sugar 
is  gradually  converted  into  alcohol,  while  carbonic  acid  escapes 
from  the  liquid.  Cane-sugar,  as  such,  does  not  undergo  this 
16 


182  FERMENTED   LIQUORS.  [§  300. 

fermentation,  but  is  first  converted  into  a  mixture  of  dextrose 
and  levulose.  Lactose,  when  pure,  is  not  susceptible  of  fermen- 
tation, although  milk  can  be  fermented.  In  this  case,  there  is 
formed  along  with  the  alcohol  a  quantity  of  an  acid  called  lactic 
acid. 

Fermented  Liquors.  —  Wines.  —  The  various  sorts  of  wines 
are  produced  by  the  spontaneous  fermentation  of  the  juice  of  grapes. 
No  yeast  is  necessary,  as  simple  exposure  to  the  air  causes  fermenta- 
tion to  set  in  (see  §  225).  Sweet  wines  are  those  in  which  there 
remains  a  portion  of  grape-sugar,  which  has  not  been  converted  into 
alcohol.  Champagne  is  wine  that  has  been  bottled  while  active  fer- 
mentation is  going  on,  and  contains  a  considerable  amount  of  carbonic 
acid  in  solution. 

Ale  and  Beer.  —  The  seeds  of  all  plants  contain  a  certain  pro- 
portion of  a  body  known  as  starch  (§  301).  By  treatment  with  very 
dilute  sulphuric  acid,  starch  may  be  converted  into  grape-sugar  (see 
Exp.  134,  §  294).  A  similar  change  takes  place  in  the  germinating 
seed  under  the  influence  of  a  substance  called  diastase,  which  is 
developed  in  the  seed.  Advantage  is  taken  of  this  fact  in  the  manu- 
facture of  ale  and  beer. 

Ale  and  beer  are  generally  prepared  from  barley.  The  grain  is 
caused  to  germinate,  by  placing  it  under  favorable  conditions  of  mois- 
ture and  temperature.  When  the  germination  has  reached  a  certain 
point,  it  is  checked  by  drying  the  grain  at  a  sufficiently  high  tempera- 
ture ;  the  product  is  now  known  as  malt,  and  the  process  is  termed 
malting.  The  malt  is  ground  and  heated  with  water  for  some  hours, 
nearly  to  the  boiling-point.  Under  the  influence  of  the  diastase  de- 
veloped in  the  grain  during  the  malting,  the  starch  is  converted  into 
dextrin  and  sugar.  To  the  infusion  thus  obtained,  the  wort,  is 
added  the  proper  amount  of  yeast,  which  causes  fermentation  to 
eet  in. 

The  proportion  of  alcohol  in  the  various  beers  and  ales  varies  from 
3  to  9  per  cent  :  beer  also  contains  some  acetic  acid,  the  various  sol- 
uble mineral  substances  of  the  grain,  some  unaltered  sugar  and 
dextrin,  some  diastase  and  coloring  matters.  The  bitter  taste  is 
imparted  by  the  addition  of  hops  before  fermentation  begins.  The 
foaming  is  caused  by  free  carbonic  acid,  the  peculiar  consistency  of 
the  foam  being  apparently  due  to  the  presence  of  dextrin. 

Other  Fermented  Liquors.  —  The  juice  of  almost  all  fruits  may 
be  fermented  with  formation  of  alcoholic  liquors  :  thus  cider  is  the 


§  303.]  STARCH.  183 

fermented  juice  of  the  apple  ;  perry  is  made  from  pears.  From  the 
juice  of  the  currant,  gooseberry,  blackberry,  etc.,  fermented  liquors 
are  obtained  popularly  called  wines.  The  South  Sea  islanders  fer- 
ment the  juice  of  the  cocoanut ;  the  Eastern  nations  obtain  an  intoxi- 
cating liquor  from  certain  palms. 

Distilled  Liquors.  —  Absolute  alcohol  may  be  obtained  by  re- 
peated distillation  of  any  fermented  liquor,  and  final  rectification 
over  quicklime  (§  227).  When,  however,  the  liquors  are  simply 
distilled,  there  is  condensed  with  the  alcohol  m^re  or  less  water, 
together  with  certain  volatile  bodies,  which  communicate  a  distinctive 
flavor  to  the  product.  Brandy  is  obtained  by  distilling  wine  :  gin  is 
spirit,  flavored  by  distilling  it  with  juniper-berries  ;  whiskey  is  pre- 
pared by  distilling  wort  made  from  corn,  rye  or  other  grain  ;  rum 
was  originally  made  by  fermenting  molasses,  and  subjecting  the  pro- 
duct to  distillation. 

301.  Starch  (CCH10O6)  is  an  organized  body  found  in  wheat, 
maize  and  all  other  grains,  in  the  tubers  of  the  potato,  in  the 
roots  and  stems,  or  in  the  fruits  of  many  other  plants.     The 
following   experiment   will   illustrate  the   manner  of   obtaining 
it  from  the  potato,  which  contains  on  the  average  20  per  cent 
of  it. 

.  Exp.  136.  —  Reduce  a  clean  potato  to  pulp  by  scraping  or  grat- 
ing ;  mix  tne  pulp  with  water,  and  squeeze  through  a  linen  or  cotton 
cloth,  repeating  the  operation  several  times.  The  woody  fibre  or 
cellulose,  of  the  potato  remains  on  the  cloth  while  the  starch  passes 
through  the  meshes,  and  remains  suspended  in  the  filtrate.  Allow 
the  liquid  to  stand  until  the  starch  has  settled,  then  pour  off  the 
water,  and  dry  the  residue. 

302.  Starch  has  the  appearance  of  a  white  powder,  but  under 
the  microscope  it  is  seen  to  be  made  up  of  distinct  rounded  or 
oval  grains,  which  vary  somewhat  in  size  and  appearance  ac- 
cording to  the  particular  plant  from  which  the  starch  was  de- 
rived.    The  grains  of  potato-starch  are  about  -$$.•$  inch  in  diame- 
ter; those  of  wheat-starch,  T(jV<y  incn  >  those  of  rice-starch  are. 
about  ^oVo  °f  an  inch.     Fig.  62  represents  the  grains  of  potato-, 
starch  very  much  magnified. 

303.  Starch  is  almost  entirely  insoluble  in  water,  but  when- 
heated  in  water  to  about  70°,  the  granules,  swell  .and  burst,  .and 


184 


STARCH.  —  DEXTRIN. 


[§  304. 


the  mixture  forms  a  jelly  or  paste  (Exp.  39,  §  93)  :  this  starch- 
Fis'  62>  paste  is    used  by  the  laun- 

dresses for  stiffening  linen. 
A  characteristic  property  of 
starch  is  its  power  of  form- 
ing a  blue  color  with  iodine 
(Exp,  39,  §  93).  By  heat- 
ing with  dilute  acid,  starch 
is  converted  into  dextrose 
(Exp.  134,  §  294). 

Inulin  is  a  substance  of  the 
same  composition  as  starch  :  it 
occurs  in  the  roots  of  the  dah- 
lia, dandelion,  chiccory  and 
other  plants  belonging  to  the  family  of  compositce.  It  exists  in  the 
plant  in  a  liquid  form,  it  is  soluble  in  hot  water,  is  not  colored  blue 
by  iodine,  and  by  heating  with  dilute  acids  is  converted  into  levulose. 
Arrow-root  and  tapioca  are  varieties  of  starch  prepared  from  the 
roots  of  tropical  plants.  Sago  is  the  starch  obtained  from  the  pith  of 
the  sago-palm.  The  peculiar  appearance  of  tapioca  and  sago  is  owing 
to  the  manner  in  which  the  starch  is  prepared,  and  these  varieties  of 
starch,  or,  rather,  successful  imitations  of  them,  are  produced  artificially 
from  ordinary  starch. 

304.  Dextrin.  —  When  starch  is  heated  to  about  205°,  it  is 
converted  into  dextrin,  a  substance  of  the  same  chemical  com- 
position as  starch,  but  differing  in  many  of  its  properties.  It  is 
soluble  in  water,  forming  a  gummy  solution,  and  is  used,  instead 
of  gum-arabic,  in  the  manufacture  of  adhesive  stamps  and  for 
other  purposes. 

Exp.  137.  —  Heat  carefully  in  a  porcelain  dish  a  teaspoonful  of 
powdered  starch  with  constant  stirring.  It  gradually  turns  brown. 
After  heating  for  about  five  or  ten  minutes,  add  four  times  its  bulk 
of  water  and  boil.  A  solution  of  dextrin  will  be  obtained,  which  may 
be  filtered  from  the  unaltered  starch.  To  a  portion  of  the  solution 
add  twice  its  bulk  of  alcohol  ;  dextrin  will  be  precipitated,  as  it  is  in- 
soluble in  alcohol. 


305.    If  starch  be  heated  for  some  time  with  water  contain- 


§  307.]  GLUTEN. -BREAD.  185 

ing  a  small  amount  of  sulphuric  acid,  the  starch  is  converted 
into  dextrin  ;  if  the  mixture  of  starch  and  water  be  heated  still 
further,  or  be  actually  boiled,  the  starch  (or  dextrin)  will  be 
converted  into  starch-sugar  (see  Exp,  134,  §  294).  This  change 
of  starch  to  dextrin  and  sugar  takes  place  in  nature  in  germinat- 
ing .^eeds  by  the  action  of  the  nitrogenous  substance  called  dias- 
tase (§  300). 

306.  Gluten.  —  It  has  been  stated  that  starch  occurs  in  the 
different  varieties  of  grain  :  its  presence  in  wheat,  as  well  as  the 
presence  of  another  body,  known  as  gluten,  may  be  shown  by 
the  following  experiment. 

Exp.  138.  —  Wet  a  handful  of  wheat  flour  with  enough  water  to 
make  a  thick  dough.  Wrap  the  dough  in  a  linen  or  cotton  cloth,  and 
knead  it  in  a  slow  stream  of  water  until  the  water  is  no  longer  ren- 
dered turbid.  The  turbidity  is  caused  by  particles  of  starch  in  sus- 
pension ;  if  a  portion  of  the  water  be  allowed  to  stand,  the  starch  will 
be  deposited,  and  may  be  recognized  by  means  of  the  iodine  test.  The 
tough,  viscous  mass  remaining  in  the  cloth  is  gluten.  In  addition  to 
these  two  substances,  the  wheat  flour  contains  a  small  amount  of 
sugar  and  dextrin,  which,  in  this  experiment,  are  dissolved  by  the 
water,  and  a  little  oil  and  woody  fibre  which  remain  with  the  gluten. 

307.  Bread. — In  the  preparation  of  bread  by  means  of  yeast, 
the  flour  is  made  into  a  dough  with  water  mixed  with  a  certain 
amount  of  yeast,  and  the  dough  left  in  a  warm  place  to  rise.     Fer- 
mentation sets  in  :  the  sugar  and  a  part  of  the  dextrin  of  the  flour 
are  gradually  converted  into  alcohol  and  carbonic  acid,  and  the  latter 
being  set  free  as  a  gas  causes  the  dough  to  swell  up  and  become 
porous.     When  the  bread  is  baked,  the  carbonic  acid  is  expanded 
still  more,  and,  as  it  escapes  from  the  bread  together  with  the  alcohol, 
which  at  the  temperature  of  the  oven  is   converted  into  vapor,  it 
communicates  the  desired  lightness  to  the  bread.     During  the  process 
of  baking,  some  water  is  also  expelled  from  the  loaf,  and  the  starch  is 
converted  into  a  gelatinous  condition.     At  the  outside  of  the  loaf 
further  decomposition  takes  place,  a  substance  like  caramel  being 
formed  which  constitutes  the  crust.     The  crust  also  contains  dextrin, 
and  if  the  outside  of  the  loaf  be  moistened  and  then  dried  in  the 
oven,  the  dextrin  thus  dissolved  and  left  again  by  evaporation  pro- 
duces a  smooth,  shining  surface. 

16* 


186  CELLULOSE.  .OH    WOODY  FIBRE.  [§  3QS. 

.308.  Cellulose  (C^H^Oj  occurs  in  all  plants  and  in  all  the 
various  parts  of  the  plant.  It  constitutes  the  outside  of  the 
cells  of  which  every  vegetable  organism  is  made  up,  and  occurs 
in  a.  .great  variety  of  forms.  The  ground-work  of  succulent 
fruits,  like  the  apple  and  pear,  of  roots  like  the  turnip  and 
beet,  as  well:  as  of  all  varieties  of  trees,  even  the  box  and,  the 
lignum-vitse,  is  cellulose.  Linen  and  cotton  are  nearly  pure 
cellulose,,  the  fibres  themselves,  being  long  .cells;  but  in  almost 
all  cases  the  cellulose  is  accompanied  by  another  substance 
which  incrusts  the  interior  of  the  cells  and  predominates  in 
the  case  of  the  harder  woods  and  in  the  shells  of  the  different 
sorts  of  nuts.  This  incrusting  substance  is  of  uncertain  com- 
position,- Tas  it  never  has  been  obtained  sufficiently  pure  for 
analysis.  It  -  is  much  more  readily  acted  upon  by  chemical 
agents^  than  cellulose,  and  by  treating  woody  fibre  with  acids 
and  alkalies,  cellulose  may  be  obtained  nearly  pure.  The  finest 
kinds  of  -filtering  (unglazed)  paper  are  nearly  pure  cellulose. 
In  Exp.  136  the  substance  remaining  in  the  cloth  was  mainly 
cellulose.  • 

The  percentage  composition  of  cellulose  is  the.  same  as  that  of 
starch,  dextrin  and  inulin,  and  would  be  most  simply  expressed  by  the 
formula  CeHJO-O5.  It  is  probable,  however,  that  the  true  formula  of 
cellulose  is  some  higher  multiple  of  these  numbers,  not  less  than 


"  309.  Pure  cellulose  is  a  white  substance  insoluble  in  water  or 
alcohol.  •  Strong  alkali  decomposes  it  with  formation  of  oxalic 
aeM  (§322)  ;  strong  sulphuric'  acid  dissolves  it,  and  on  diluting 
the  solution,  and  boiling,,  the  cellulose  is  converted  first  into 
dextrin  and  finally  into  grape-sugar.  By  short  contact  with 
sulphuric  acid  of  a  particular  strength,  cellulose  is  converted 
into  a  semi-transparent,  tough  .  substance  resembling  animal 
membrane.  Paper  thus  treated  is  changed  into  a  substance 
known  as  vegetable  parchment. 

Exp.  139.  —  To  10  c.  c.  of  water  in  a  porcelain  dish  add  slowly, 
with  .constant,  stirring,  .25  c.  c.  of  strong  sulphuric  acid.  When  the 
mixture  has  become  perfectly  cold,  immerse  in  it  a  piece  of  filtering- 


I  3 1 1 .  ]  'O  UN-GO  TTON.  -  Q  VMS.  18  7 

paper.  Allow  the  paper  to  remain  in  the  liquid  for  15  or  20  seconds  ; 
then  remove  and  rinse  thoroughly  to  remove  the  acid,  first  with  pure 
water,  then  with  water  containing  a  little  ammonia,  and  finally  with 
pure  water  again.  The  paper  is  converted  into  vegetable  parchment. 
If  the  first  experiment  be  not  successful,  repeat  \vith  fresh  pieces  of 
paper,  varying  the  time  of  immersion  until  a  good  result  is  obtained. 

310.  By  treatment  with  a  mixture  of  nitric  and  sulphuric 
acids,  cellulose  is  converted,  without  change  of  form^  into  a  com- 
pound called  nitro-cellulose,  pyroxylin  or  gun-cotton,     This 
substance  is  very  explosive,  although  not  nearly  as  much  so  as 
nitro-glycerin,  which  is  prepared  from  glycerin  in  a  similar 
manner.     In  the  air  it  burns  with  a  sudden  flash  without  smoke. 
If  burned  in  a  confined  space,  it  produces  explosive  effects  simi- 
lar to  those  produced  by  gunpowder. 

Gun-cotton  is,  chemically  speaking,  cellulose  in  which  a  certain 
number  of  atoms  of  hydrogen  are  replaced  by  a  corresponding  num^ 
ber  of  atoms  of  the  radical  NO2.  Its  exact  composition  differs  ac- 
cording to  the  strength  and  proportions  of  the  "acids  used  in  its  forma- 
tion, there  being  several  distinct  varieties. 

Collodion  is  the  name  given  to  the  .solution  of  a  certain  variety 
of  pyroxylin  in  a  mixture  of  alcohol  and  ether.  When  this  solu- 
tion is  exposed  to  the  air  in  a  thin  layer,  the  solvent  rapidly  evap- 
orates and  leaves  a  transparent  film  of  pyroxylin.  Collodion  is  much 
used  by  photographers. 

311.  Gum.  —  Gum-arabic  is  a  familiar  example  of  a  class  of 
bodies  which  occur  in  the  juice  of  almost  all  plants.     Gum-arabic 
exudes  from  a  species  of  acacia.     It  is  valuable  chiefly  on  ac- 
count of  forming  with  water  a  sticky,  mucilaginous  liquid. 

The  gums  are  soluble  in  water,  but  insoluble  in  alcohol,  as 
may  be  illustrated  in  the  case  of  gum-arabic  by  the  following 
experiment. 

Exp.  140.  —  Dissolve  10  grms.  of  gum-arabic  in  75  c.  c,  of  water. 
The  solution  is  facilitated  by  powdering  the  gum-arabic,  mixing  it 
with  clean  dry  sand  and  stirring  the  mixture  from  time  to  time. 
When  solution  has  been  effected,  allow  the  sand  to  settle  and  pour 
off  the  liquid. 

To  a  portion  of  the  solution  thus  prepared,  add  half  its  bulk  of 
alcohol  :  the  gum  is  reprecipitated. 


188  PECTOSE  AND   PECTIN.  [§  312. 

312.  Gum-arabic   is  a  mixture  of  the  calcium   and  potas- 
sium salts   of  arable   acid ;    calcium   and   potassium   arabates 
are    soluble    in   water :    many   other  arabates   are   insoluble   in 
water. 

Exp.  141.  —  To  a  portion  of  the  solution  of  gum-arabic  of  Exp. 
140  add  an  arnmoniacal  solution  of  lead  acetate  (prepared  by  adding 
to  an  aqueous  solution  of  lead  acetate  ammonia- water  in  quantity 
insufficient  to  produce  a  precipitate)  :  a  white  precipitate  of  an  ara- 
bate  of  lead  is  formed. 

To  the  class  of  gums  belong  the  exudations  from  trees  like  the 
cherry,  peach  and  plum  ;  but  the  substances  which  exude  from  pines 
and  similar  trees,  often  called  gum,  as  spruce  gum,  for  example,  belong 
to  a  different  class  of  bodies,  —  that  of  the  resins  (§  316). 

Gum-tragacanth  is  a  modification  of  ordinary  gum.  When  treated 
with  water,  it  swells  up,  but  does  not  dissolve  :  4  or  5  grms.  of  this 
gum  are  sufficient  to  convert  a  litre  of  water  into  a  pasty  mass. 
Similar  to  gum-tragacanth  is  vegetable  mucilage,  a  substance  which 
occurs  in  the  root  of  the  marsh-mallow,  and  also  in  flaxseed  and  the 
seeds  of  the  quince. 

313.  Pectose,  —  In  the  flesh  of  unripe  fruits,  and  in  such 
roots  as  the  turnip,  beet,  carrot,  etc.,  there  exists,  along  with 
the  cellulose  (§  308),  a  body  to  which  the  name  of  pectose  has 
been  given.     It  has  as  yet  been  impossible  to  separate  this  sub- 
stance from  the  cellulose,   and  its  existence   has   been   rather 
inferred  from  the  products  of  its  transformation  than  proved 
by  actual  isolation.     By  the  ripening  of  the  fruit,  or  under  the 
influence  of  heat,  acids  or  other  chemical  agents,  the  pectose  is 
changed  into  pectin,  a  substance  soluble  in  water,  but  insoluble 
in  alcohol. 

Exp.  142.  —  Reduce  several  white  turnips  or  beets  to  pulp,  by 
grating.  Enclose  the  pulp  in  a  piece  of  cotton  cloth,  and  wash  by 
squeezing  in  water,  until  all  the  soluble  matters  have  been  removed,  or 
until  the  water  comes  off  nearly  tasteless.  To  the  washed  pulp,  add 
enough  dilute  chlorhydric  acid  (1  part  by  measure  of  the  strong  acid 
to  15  parts  of  water)  to  saturate  the  mass,  and  allow  it  to  stand  for 
48  hours.  At  the  end  of  that  time,  squeeze  out  the  acid  liquid,  filter 
it,  and  add  an  equal  bulk  of  alcohol.  Pectin  will  separate  as  a  gelat- 
inous, stringy  mass. 


[§  316.  BALSAMS.  — RESINS.  189 

314.  The  viscid  gummy  juice  which  oozes  from  baked  apples 
is  a  strong  solution  of  pectin.     The  various  sorts  of  fruit-jellies 
are  composed  of  other  products  of  the  transformation  of  pectose 
(pectic  and  pectosic  acids). 

Exp.  143.  —  Stew  a  handful  of  sound  cranberries  covered  with 
water  just  long  enough  to  make  them  soft.  Observe  the  speedy  solu- 
tion of  the  firm  pectose.  Strain  through  a  cloth.  The  juice  con- 
tains dissolved  pectin,  which  may  be  precipitated  by  the  addition  of 
alcohol  to  a  portion  of  the  juice.  Heat  the  remainder  of  the  juice 
in  a  flask  on  the  water-bath  (see  Appendix,  §  17).  After  a  time, 
which  is  variable  according  to  the  condition  of  the  fruit,  and  must 
be  ascertained  by  trial,  the  juice  on  cooling  or  standing  solidifies  to 
a  jelly  that  dissolves  on  warming,  and  re-appears  on  cooling  ;  this 
jelly  is  pectosic  acid.  By  further  heating,  the:  e  may  be  formed  a 
jelly  which  is  permanent  when  hot ;  this  jelly  is  pectic  acid. 

315.  Balsams.  —  The  term   balsam  is  applied  to  the   soft 
viscid  substances  which  exude  from  the  bark  of  certain  trees, 
or  are  obtained  in  greater  quantity  by  making  incisions  into 
the  wood  of  the  trees.      Canada  balsam,  balsam  of  Copaiba, 
spruce  gum  and  ordinary  turpentine  are  examples  of  this  class 
of  bodies.     The  balsams  are  complex  substances  :  they  consist 
in  the  main  of  an  essential  oil  which  holds  in  solution  bodies 
of  peculiar  character  known   as   resins.      When   the   balsams 
are  distilled  with  water,  the  essential  oil  passes  over  with  the 
steam,  and  the  resin  remains  behind.     This  fact  has  already 
been  illustrated  in  Exp.  116,   and  in  this  experiment  it  was 
seen  that  after  the  distillation  there  remained  in  the  retort  a 
substance  which,   although  quite  fluid  at  the  temperature  of 
boiling  water,  solidified  on  cooling  to  a  vitreous  semi-transparent 
mass  :  it  was  common  rosin,  a  familiar  example  of  the  class  of 
resins. 

316.  Resins.  —  The  resins,   as   has  been  stated  above,  are 
generally  obtained  by  making  incisions  in  the  wood  of  the  trees 
by  which  they  are  produced.     From  these  incisions  they  exude 
mixed  with  the  essential  oil  of  the  plant.     Common  rosin,  which 
belongs  to  this  class,  is  the  vitreous  mass  left  on  distilling  crude 
turpentine  with  water  (see  Exp.  116,  §  251).     It  burns  with  a 


190  REStm-&UTTA-PE&CHA.  [-§317. 

smoky  flame,  and  is  used  in  the  preparation  of  lamp-black 
(§  181)  and  cheap  varnish.  Gum  copal,  mastic,  sandarach  and 
shellac  are  resins.  The  resins  are  insoluble  in  water,  but  dis- 
solve in  alcohol,  wood  naphtha  (§  230),  naphtha  and  oil  of 
turpentine.  -  The  solutions  thus  obtained  are  called  varnishes. 
When  exposed  in  a  thin  layer  to  the  air,  the  solvent  evaporates, 
leaving  a  transparent  coating  of  the  resin,  which  protects  the 
varnished  surface  from  air  and  moisture. 

Exp.  144.  —  Powder  3  grms.  of  shellac,  mix  with  a  quantity  of 
clean  sand  and  pour  upon  it  30  c.  c.  of  alcohol.  Allow  to  stand  until 
the  shellac  has  dissolved.  Pour  a  portion  of  the  solution  into  water  : 
the  shellac  is  precipitated;  as  it  is  insoluble  in  water. 

317.  The  resins  seem  in  many  cases  to  be  formed  by  the  oxidation 
of  the  essential  oil  of  the  plant  by  which  they  are  produced,  and  it  is 
a  familiar  fact  that  when  oil  of  turpentine  is  exposed  to  the  air  it 
absorbs  oxygen,  and  is  converted  into  a  sticky,  resinous  substance. 
During  the  oxidation  ozone  is  produced,  and  its  effects  are  manifested 
by  its  bleaching  action  on  the  corks  of  the  bottles  in  which  the  oil  of 
turpentine  is  kept. 

The  resins  are  made  up  in  the  main  of  several  acid  bodies,  of 
which  resinic  acid  is  the  principal.  By  the  action  of  bases  on  resin, 
bodies  called  resinates.  are  formed  ;  thus  sodium  resinate,  formed  by 
the  action  of  caustic  soda  on  common  rosin,  is  used  in  the  manufac- 
ture of  -some  kinds  of  soap  ;  it  is  soluble  in  water  and  valuable  on 
account  of  its  -detergent  properties/  Lead  resinate  is  insoluble  in 
water  and  alcohol. 

Exp.  145.  — "Dissolve  a  small  amount  of  powdered  rosin  in  alcohol  : 
prepare  also  an  alcoholic  solution  of  acetate  of  lead  by  dissolving  a 
portion  of  the  crystallized  salt  in  10  times  its  bulk  of  alcohol.  Mix 
the  two  solutions  and  observe  the  formation  of  a  bulky  white  precipi- 
tate of  lead  resinate. 

318.  Gum  Resins  are  exudations  from  many  plants  which, 
being  first  milky,  afterwards  solidify  in  the  air.-    Gutta-percha 
is  a  tough,   elastic  substance  insoluble  in  water,  which  issues 
as  a  milky  juice  from  cuts  in  the  trunk  of  a  species  of  tree 
which  grows  in  the  East  Indies.     Gutta-percha  is  a  mixture 
of    a    hydrocarbon    (C20H32)    and    several   resins.      Caoutchouc 
oi'  India-rubber    is    the    solidified,   juice... of   certain,  tropical. 


321'.] 


CAOUTCHOUC.  '--VEGETABLE  ACIDS. 


plants.  It  is  mainly  a  mixture"  of  several'  hydrocarbons 
(x  C5H8).  It  is  insoluble  in  water,  but  when  treated  with 
ether,  carbon  bisulphide,  oil  of  turpentine  or  benzol,  it  swells 
up  in  a  very  remarkable  manner,  and  finally  forms  a  sort  of 

solution. 

Bxp.  146.  —  Into  a  small  bottle  put  several  teaspoonfuls  of  oil  of 
turpentine,  and  add  a  few  clippings  of  sheet  caoutchouc.  Cork  the 
bottle  and  allow  it  to  stand  for  some  time.  The  caoutchouc  swells 
up  to  many  times  its  original  bulk,  and  eventually  dissolves. 

319.  Caoutchouc  is  very  elastic,  and  freshly-cut  edges  readily 
reunite.     When  exposed  to  the  light  and  air  for  some  time,  it 
absorbs  oxygen  and  is  converted  into  a  sticky  mass.     Caout- 
chouc may  be  made  to  take  up  and  combine  with  a  certain  pro- 
portion of  sulphur,   forming  what  is  called  vulcanized  India- 
rubber.     This  mixture  preserves  its  consistency  and  its  elasti- 
city through  all  ordinary  changes   of  temperature,   and  is  not 
affected  by  exposure  to  light.     Heated  to  a  certain  temperature, 
the  vulcanized  caoutchouc  is  converted  into  a  hard  mass  resem- 
bling   horn,    and    called  "hard    rubber,"   vulcanite   or  ebonite. 
India-rubber  and  gutta-percha  are  largely  used  in  the  manufac- 
ture of  water-proof  clothing,  tubing  for  conveying  liquids  and 
gases,  combs,  buttons,  picture-frames  and  a  great  variety  of  other 
articles. 

320.  Amber  is  one  of  a  number  of  fossil  substances  resem- 
bling the  resins.     Amber  is  found  principally  along  the  shores 
of  the  Baltic,  but  also  occurs  in  beds  of  lignite  in  other  locali- 
ties.    It  becomes  highly  electric  on  friction.     Chemically  it  is  a 
mixture  of  several  resinous  bodies  ;  it  also  contains  a  peculiar 
acid  called  succinic  acid.     Only  about  an  eighth  part  is  in  its 
natural  state   soluble  in  alcohol  ;    but  after  fusion  it  dissolves 
quite  readily  and  is  used  in  the  preparation  of  varnish. 

321.  Vegetable  Acids.  —  Among  the  important  products  of 
the  vegetable  kingdom  are  the  organic  acids  which  occur  ready 
formed  in  plants,  either  in  the  free  state  or  in  combination,  as 
salts  of  certain  metallic  elements  or  radicals.     The  occurrence  of 
the  salts  of  several  of  the  fatty  acids  in  the  oils  of  plants  has 


192  OXALIC  ACID.  [j  322. 

already  been  noticed.  The  salts  of  oleic  acid  (§  241)  and  other 
acids  classed  with  it  also  exist  in  vegetable  fats  and  oils.  The 
acids  which  are  to  be  considered  in  this  place  generally  occur 
as  salts  of  calcium  or  potassium. 

322.  Oxalic  acid  (C2H2O4)  occurs  as  potassium  oxalate  and 
calcium   oxalate  in  the  juice  of  the  sorrel,  rhubarb  and  many 
other  plants.     Calcium  oxalate,   though  insoluble  in  water,  is 
somewhat  soluble  in  the  juices  of   the  plant :  it  is,  however, 
sometimes    found  in   microscopic  crystals  in   the   cells  of  the 
plant.     Oxalic  acid  is  very  poisonous  when  taken  internally  ; 
the  best  antidote  is  chalk  (calcium  carbonate)  or  magnesia,  as 
the  oxalates  of  calcium  and  magnesium  are  quite  insoluble  com- 
pounds. 

323.  On  a  large  scale  oxalic  acid  is  prepared  by  making  a 
thick  paste  of  sawdust  with  a  strong  solution  of  caustic  potash 
and  caustic  soda  and  heating  the  mixture  on  iron  plates.     The 
woody   fibre   is    converted    into    oxalic   acid,  and  sodium   and 
potassium  oxalates  are  formed  from  which  the  acid  is  extracted. 
On  a  small  scale  oxalic  acid  is  best  prepared  by  the  action-  of 
nitric  acid  on  starch  or  sugar. 

Exp.  147.  —  In  a  flask  of  500  c.  c.  capacity,  heat  gently  100  c.  c. 
of  nitric  acid  of  1.38  sp.  gr.  and  10  grins,  of  starch.  The  experiment 
should  be  performed  where  there  is  a  good  draught  of  air,  as  nitrous 
fumes  are  copiously  evolved.  When  the  evolution  of  the  fumes  has 
nearly  ceased,  the  solution  is  transferred  to  an  evaporating  dish  and 
slowly  evaporated  to  about  one-sixth  its  bulk.  On  cooling  the  solu- 
tion, oxalic  acid  will  be  obtained  in  transparent  crystals. 

324.  Oxalic    acid    occurs   in    crystals    having    the    formula 
C2H2O4  -j-  2  H2O.     The  crystals   lose  the  water  of    crystalliza- 
tion when  dried  at  100°,  and  at  the  ordinary  temperature  of 
the  air  they  effloresce  somewhat.     The  crystals  are  much  more 
soluble  in  hot  than  in  cold  water.     Oxalic  acid  dissolves  the 
metallic  oxides  with  facility,   forming  oxalates :    on  this   fact 
depends  its  use  in  cleaning  articles  of  brass  and  copper,  and  in 
removing  spots  of  iron-rust  and  ink. 

Exp.   148.  —  Dip  a  piece  of  white  cloth  in  common  writing-ink, 


§327.]  MALIC  ACID.-  TARTARIC  ACID.  193 

and  when  dry  immerse  it  in  a  solution  of  oxalic  acid,  made  by  dis- 
solving 2.5  grms.  of  oxalic  acid  in  50  c.  c.  of  water.  Then  rinse  the 
cloth  in  water  :  the  color  will  be  discharged. 

Writing-ink  owes  its  color  to  a  tannate  of  iron  (§  331),  which  on 
exposure  to  the  air  becomes  nearly  insoluble  in  water.  The  oxalic 
acid  destroys  this  compound  and  forms  with  the  iron  a  soluble  com- 
bination. 

325.  From   the   formula   of    oxalic   acid,    C2H2O4(H2O,C2O3),  the 
existence  of  an  anhydride  C2O3  might  be  inferred,  an  oxide  of  car- 
bon intermediate  between  CO  and  CO2.     Such  anhydride  has,  how- 
ever, never  been  obtained.     When  oxalic  acid  is  treated  with  strong 
sulphuric  acid  it  is  broken  up,  the  sulphuric  acid  retaining  the  HaO, 
and  the  C2O3  dividing  into  CO  and  CO2.     In  fact,  this  is  a  common 
way  of  making  carbon  protoxide.     By  distilling  alcohol  with  oxalic 
acid,  oxalic  ether  or  ethyl  oxalate  is  obtained  (C2H5)2C2O4. 

326.  Malic  acid  (C4H6O5)  occurs  abundantly  in  unripe  apples, 
and  in  most  acid  fruits,  such  as  the  gooseberry  and  currant.     As 
potassium  malate,  it  occurs  in  the  rhubarb,  and  crystals  of  this 
salt  may  be  obtained  by  evaporating  the  juice  of  the  leaf-stalks. 
Calcium  malate  occurs  in  sumach  berries  and  in  the  sap  of  the 
maple.     In  boiling  down  the  maple  sap  to  obtain  the  sugar,  fine, 
hard  crystals  of  calcium  malate  often  separate.     Malic  acid  may 
be  obtained  in  crystals,  but  they  are  extremely  soluble  in  water, 
and  deliquesce  in  moist  air. 

327.  Tartaric   Acid  (C4H6O6).  —  Tartaric  acid   occurs  in  a 
great  variety  of  plants  :  the  commercial  supply  is  obtained  from 
the  grape.     All  varieties  of  wine  during  fermentation  deposit 
on  the  insides  of  the  casks  a  crust  called  argol.     This  argol  or 
crude  tartar  is  a  hydrogen  potassium  tartrate,  commonly  called 
"  bitartrate  of  potash ;  "  when  purified,  it  is  called  "  cream  of 
tartar :  "  from  argol  or  cream  of  tartar  tartaric  acid  itself  may 
be  obtained  in  transparent  crystals,  which  are  permanent  in  the 
air. 

Exp.  149.  —  Dissolve  20  grms.  of  cream  of  tartar  in  150  c.  c.  of 

iiot  water,  to  which  10  c.  c.  of  strong  chlorhydric  acid  have  been 
added.  To  the  solution  add  milk  of  lime  (made  by  stirring  20  grms. 
of  slaked  lime,  calcium  hydrate,  into  100  c.  c.  of  water)  until  the 
solution  shows  a  distinctly  alkaline  reaction.  Insoluble  calcium  tar- 
17 


194  TARTARIC  ACID.  -TANNIN.  [§328. 

trate  settles  to  the  bottom  of  the  liquid,  and  should  be  collected  on  a 
filter  and  washed.  Transfer  this  calcium  tartrate  to  a  flask,  add  100 
c.  c.  dilute  sulphuric  acid  (made  by  adding  10  grms.  oil  of  vitriol  to 
100  c.  c.  water),  and  boil  for  some  minutes.  The  sulphuric  acid 
causes  the  formation  of  calcium  sulphate,  and  free  tartaric  acid  is  left 
in  the  liquid.  The  insoluble  calcium  sulphate  is  removed  by  nitration  ; 
the  filtrate  is  concentrated  by  evaporation  over  the  lamp  to  the  bulk 
of  20  c.  c.  and  allowed  to  cool.  Crystals  of  tartaric  acid  separate 
from  the  liquid.  These  crystals  are  drained  from  the  mother  liquor 
and  pressed  between  pieces  of  filter-paper  ;  they  may  be  purified  by 
dissolving  them  in  half  their  weight  of  boiling  water,  and  allowing 
the  solution  to  cool,  when  a  considerable  part  of  the  acid  crystallizes 
out  again. 

328.  Tartaric  acid  finds  important  applications  in  the  art  of 
dyeing,  and  many  of  the  tartrates  are  important  compounds  : 
Rochelle  salt  is  a  sodium  potassium  tartrate  :  tartar  emetic  is  an 
antimony  potassium  tartrate ;  both  these  salts  are  used  in  medi- 
cine.    The  so-called  "  Rochelle  powders  "  contain  cream  of  tar- 
tar in  one  paper,  and  hydrogen  sodium  carbonate  in  the  other ; 
when  the  two  materials  are  mixed  in  water,  carbonic  acid  is  set 
free,  and  Eochelle  salt  remains  in  solution. 

Exp.  150.  —  Dissolve  10  grms.  cream  of  tartar  in  175  c.  c.  of  hot 
water,  and  to  the  solution  add  a  strong  solution  of  sodium  carbonate 
as  long  as  the  addition  produces  effervescence.  Evaporate  the  solution 
over  the  lamp  to  the  bulk  of  20  c.  c.  and  then  allow  it  to  cool.  Crys- 
tals of  Rochelle  salt  will  be  obtained. 

329.  Citric  acid  (C6H8O7)  occurs  very  abundantly  in  the  juice 
of  the  lime  and  the  lemon,  and  has  been  found  in  the  tomato 
and  in  most  acid  fruits.     It  may  be  obtained  crystallized,  with 
one  equivalent  of  water,  in  large  transparent  crystals.     It  has  a 
sour,  but  rather  agreeable  taste.     It  is  used  by  the  calico-print- 
ers, and  to  some  extent  in  medicine,  especially  as  magnesium 
citrate.  ,  ** 

330.  Tannic  Acid.  —  Tannin  is  the  general  name  applied 
to  an  astringent  principle  contained  in  the  leaves  and  bark  of 
many  forest  trees,  such  as  the  oak,  hemlock  and  pine.     Simi- 
lar substances    occur   in   the   leaves   and  bark  of  many  fruit- 


§  332.]  TAN  NIC  ACID.  195 

trees,  in  the  roots  of  certain  plants,  as  well  as  in  coffee  and 
tea.  These  substances  possess  an  acid  reaction,  and  several 
distinct  acids  have  been  identified  in  them ;  the  tannin  derived 
from  gall-nut  is  called  gallo-tannic  acid;  that  from  oak  bark 
is  called  querci-tannic  acid;  that  from  coffee,  caffeo-tannic 
acid. 

331.  The  principal  applications  of  tannic  acid  in  the  arts 
are  in  the  preparation  of  writing-ink,  and  in  the  manufacture  of 
leather. 

Exp.  151.  —  Boil  10  grms.  of  powdered  nut-galls  in  about  60  c.  c. 
of  water  for  several  hours,  replacing  from  time  to  time  the  water 
lost  by  evaporation  :  a  solution  of  tannic  acid  is  thus  obtained.  Allow 
the  mixture  to  settle,  and  decant  the  clear  liquid  into  a  clean  bottle. 
To  a  portion  of  this  solution  add  a  few  drops  of  a  solution  of  cop- 
peras (iron  sulphate).  A  violet-colored  precipitate  is  formed,  which 
gradually  changes  to  black  ;  it  is  an  iron  tannate.  If  the  solution  of 
tannic  acid  were  made  viscous  by  the  addition  of  a  little  gum,  the 
precipitate  would  remain  suspended  in  the  liquid.  Common  ink  is 
made  from  these  materials. 

Exp.  152.  —  To  another  portion  of  the  tannic  acid  solution,  add 
a  few  drops  of  a  solution  of  gelatin  or  isinglass.  A  copious  white 
gelatinous  precipitate  falls. 

On  the  property  just  illustrated,  of  uniting  with  gelatinous 
matters  to  form  insoluble  compounds,  depends  the  use  of  tannic 
acid  in  tanning.  If  a  piece  of  raw  hide  from  which  the  hair 
has  been  removed  be  immersed  in  an  infusion  of  the  bark,  the 
gelatinous  matters  of  the  hide  gradually  remove  the  tannic  acid 
from  the  solution,  and  combine  with  it  to  form  an  insoluble 
compound,  which  remains  in  the  structure-of  the  hide  :  the  skin 
thus  altered  is  leather. 

332.  In  Exp.  151,  it  was  seen  that  a  solution  of  a  salt  of  iron 
was  blackened  by  the  addition  of  a  solution  of  tannic  acid  de- 
rived from  gall-nuts.     This  reaction  may  be  made  use  of  as  a 
test  to  demonstrate  the  presence  of  tannic  acid. 

Exp.  153.  —  Boil  a  few  tea-leaves  in  a  small  amount  of  water, 
and  to  the  liquid  add  a  drop  or  two  of  a  solution  of  copperas.  The 
liquid  is  blackened,  and  after  a  time  a  black  precipitate  of  iron  tan- 


196  THE    VEGETABLE  ALKALOIDS.  [§  33$. 

nate  subsides.  The  presence  of  tannic  acid  may  be  shown  similarly 
in  coffee,  in  hemlock  bark,  in  horse-chestnut  husks,  etc. 

333.  Gallic  Acid. —  The  gall-nuts  used  in  Exp.  151  are  excres- 
cences produced  on  a  species  of  oak  by  the  punctures  of  a  certain  in- 
sect. Besides  tannic  acid,  the  nut-galls  contain  a  small  percentage 
of  another  acid,  gallic  acid.  Gallic  acid  may  also  be  produced 
by  boiling  a  solution  of  tannic  acid  (from  nut-galls)  with  dilute  sul- 
phuric acid.  The  composition  of  gallo-tannic  acid  is  C^H^C^  ;  when 
boiled  with  dilute  sulphuric  acid,  it  unites  with  the  elements  of  water, 
and  forms  gallic  acid  and  glucose  (§  294). 

C27H22017  +  4  H20  -  3  C7H605  +  C6H12O6. 
Tannic  acid.  Gallic  acid.  Glucose. 

Tannic  acid  is  the  representative  of  a  class  of  bodies,  which,  by  a 
reaction  analogous  to  that  represented  above,  yield  glucose  :  they  are 
hence  called  glucosides. 

334.  The  Vegetable  Alkaloids   or  organic  bases  occur  in 
small  quantities  in  various  plants  of  which  they  constitute  the 
medicinal  or  poisonous  principles.     They  occur  in  combination 
with  some  acid  which  is  generally  peculiar  to  the  particular 
plant  in  which  they  are  found.     They  are  only  slightly  soluble 
in  water,  but  are  readily  dissolved  by  alcohol.     They  resemble 
ammonia  in  containing  nitrogen,  in  having  an  alkaline  reaction, 
and  in  uniting  directly  with  acids  to  form  salts,  which  as  a  rule 
crystallize  readily. 

335.  Opium  is  the  dried  juice  of  the  poppy.     It  contains 
besides  certain  gummy,  resinous  and  oily  bodies  no  less  than  six 
alkaloids  in  combination  with  a  peculiar  acid  called  meconic  acid. 
Of  these  alkaloids  morphia,  or  morphine,  is  the  most  important 
as  a  medicinal  agent.     It  is  usually  administered  as  sulphate  or 
chloride.     Morphine  er  opium  in  small  doses  acts  as  a  sedative, 
in  large  doses  as  a  narcotic  poison. 

Strychnine  is  a  highly-poisonous  alkaloid  which  occurs  in 
the  St.  Ignatius  bean  and  in  the  nux  vomica,  associated  with 
brucine.  Of  the  two,  strychnine  is  the  more  violent  poison, 
although  both  are  very  powerful  in  their  effects  on  the  living 
organism. 

The  bark  of  the  cinchona,  a  tree  found  native  in  Peru,  con- 
tains several  bases,  of  which  the  most  important  are  quinine 


§  337.]  ORGANIC  COLORING  MATTERS.  197 

and  cinehonine.  Quinine  possesses  valuable  medicinal  proper- 
ties, and  is  used  as  a  febrifuge ;  cinehonine  is  also  employed  as 
a  medicine,  but  is  of  less  value  than  quinine. 

Caffeine  or  Theine  occurs  in  tea  and  coffee,  and  may  be  ob- 
tained therefrom  in  white  crystals  ;  theobromine  occurs  in  cacao ; 
nicotine  is  the  chief  alkaloid  in  tobacco,  and  is  a  very  violent 
poison. 

336.  Organic  Coloring  Matters,  —  Nearly  all  of  the  organic 
coloring  matters  used  in  dyeing  are  of  vegetable  origin.     They 
occur  sometimes  in  the  roots,  sometimes  in  the  stems  or  bark, 
sometimes  in  the  flowers  or  even  in  the  seeds  of  the  plant  from 
which  they  are   derived.      Some  coloring  matters  occur  ready 
formed  in  the  plant,  others  are  the  result  of  the  action  of  the 
air  or  some  other  chemical  agent  upon  natural  products.     These 
substances  in  many  cases  are  not   chemically  related  to   each 
other,  but  they  are  classed  together  on  account  of  their  associa- 
tion in  the  arts.     A  few  of  the  more  important  will  be  here 
mentioned. 

337.  Madder  is  the  root  of  a  plant  grown  extensively  in  the 
East,  in  the  south  of  France  and  in  some  other  localities  in  Eu- 
rope.    It  is  used  principally  in  dyeing  reds  and  purples.     The 
coloring  matters  do  not  exist  ready  formed  in  the  plant,  but  are 
produced  by  the  decomposition  of  a  body  contained  in  it.     The 
principal  coloring  matter,  and  the  one  to  which  madder  owes  its 
value,  is  a  substance  called  alizarin. 

By  the  action  of  reducing  agents  alizarin  (C14H8O4)  is  converted 
into  a  hydrocarbon  identical  with  anthracene  (C14H10),  a  compound 
occuring  in  coal-tar  (§  281)  ;  and  recently  chemists  have  succeeded 
in  preparing  alizarin  artificially  from  anthracene. 

Among  other  organic  coloring  matters  used  in  dyeing  various 
red  dyes  are  Brazil-wood,  logwood,  safflower  and  cochineal.  The 
last  is  a  dried  insect,  which,  when  alive,  lives  on  a  tropical  plant, 
a  species  of  cactus.  The  coloring  matter,  carmine,  is  soluble  in 
water.  • 

Exp.  154.  —  Boil  2  grms.  of  crushed  granules  of  cochineal  in 
75  c.  c.  water  for  some  minutes.  Filter  the  colored  solution  and  pre- 
serve for  use  in  subsequent  experiments, 


198  DYEING,  [5  338i 

338.  Yellow    dye-stuffs   are   quercitron,    obtained    from    the 
bark  of  a  variety  of  oak,  fustic,  from  the  wood  of   a  West- 
Indian  tree,  turmeric  from  the  root  of  an  East-Indian  plant, 
and  a  coloring  matter  obtained  from  "  Persian  berries."     Cer- 
tain species  of  lichens  also  yield   coloring   matters  \   the  dye- 
stuffs    known  as  archil,  cudbear  and   litmus  are   derived  from 
such  sources. 

339.  Dyeing.  —  One  method  of  dyeing  fibres  or  fabrics  of 
animal  and  vegetable  origin  has  been  illustrated  by  Exp.  130, 
in  which  simple  immersion  of  the  wool  in  the  solution  of  picric 
acid  sufficed  to  give  it  a  yellow  color. 

Exp.  155.  —  Into  a  warm  solution  of  picric  acid  prepared  as 
directed  in  Exp.  130  put  a  piece  of  cotton  cloth  or  a  skein  of  cotton 
yarn.  After  the  cotton  has  been  immersed  in  the  solution  for  some 
time,  take  it  out  and  rinse  it  with  water.  It  will  be  found  that  the 
cotton  is  not  colored. 

This  experiment  illustrates  a  very  important  difference  be- 
tween the  fibres  of  vegetable  and  those  of  animal  origin.  Of 
almost  all  the  vegetable  coloring  matters,  it  is  true,  that  they  do 
not  directly  produce  fast  colors  on  cotton  or  linen,  while  they 
readily  color  articles  of  wool. 

Exp.  156.  —  Prepare  a  solution  of  the  coloring  matter  of  log- 
wood by  dissolving  1  grm.  of  extract  of  logwood  in  75  c.  c.  water. 
Allow  the  liquid  to  stand  for  a  short  time  until  it  becomes  nearly 
clear,  and  then  decant  it  from  any  insoluble  matter  which  may  sub- 
side. Place  a  quantity  of  the  nearly  clear  solution  in  a  porcelain 
evaporating-dish,  put  into  it  a  piece  of  cotton  cloth  5  or  6  c.  m.  square 
and  boil  for  some  10  minutes.  On  removing  the  cloth,  it  will  be 
found  possible  to  wash  out  most  of  the  dye,  leaving  the  cloth  only 
slightly  colored. 

Exp.  157.  —  Into  a  quantity  of  logwood  solution  equal  to  that 
employed  in  the  last  experiment,  put  a  piece  of  cotton  cloth  5  or  6 
c.  m.  square  which  has  previously  been  soaked,  first  in  a  solution  of 
common  alum,  and  then  in  ammonia-water.  Boil  the  solution,  as  in 
.the  previous  experiment.  When  the  cloth  is  removed,  it  will  be  found 
to  be  quite  strongly  colored. 

This  experiment  illustrates  the  fact  that  it  is  possible  to  impregnate 
the  cloth  with  certain  substances  which  have  the  power  of  dragging 


§  342.]  1ND1QO-&LVE  AND   WHITE  INDIOO.  190 

in  the  coloring  matter  and  holding  it  firmly.  Such  substances  are 
called  mordants,  and  as  they  are  generally  compounds  of  some  of 
the  metals,  their  action  will  be  better  studied  hereafter  (§  451). 

340.  Indigo.  —  Of  the  vegetable  dyes,  one  of  the  most  im- 
portant, and  one  which  possesses  considerable  chemical  interest, 
is  indigo  used,  as  is  well  known,  in  producing  a  very  permanent 
blue  color.     Crude  indigo  contains  a  blue  coloring  matter  which, 
when  purified,  is  known  as  indigotin  or  indigo-blue.     Its  for- 
mula is  Ci6HioNiO2,  arid  it  differs  from  the  other  coloring  mat- 
ters previously  mentioned  in  that  it  contains  nitrogen.     The  blue 
coloring-matter  does  not  occur  ready  formed  in  the  plant,  but  is 
produced  by  a  sort  of  fermentation.     Indigo-blue  is  insoluble  in 
water  or  in  alkaline  liquids,  but  dissolves  in  fuming  sulphuric 
acid  (§  135),  forming  a  deep  blue  solution. 

Exp.  158. — Upon  1  grin,  of  finely  powdered  indigo  pour  6  grms.  of 
fuming  sulphuric  acid  and  let  the  mixture  stand  for  some  hours  in  a 
warm  place.  On  the  addition  of  water  a  deep  blue  solution  is  ob- 
tained. Ordinary  strong  sulphuric  acid  will  dissolve  indigo,  but  it  is 
necessary  to  take  a  much  larger  quantity  (in  this  case  about  12  or  14 
grms.),  and  to  heat  the  mixture  to  about  60°  ;  moreover,  when  thus 
heated  a  portion  of  the  blue  coloring-matter  is  destroyed. 

341.  The  deep  blue  liquid  formed  by  the  action  of  sulphuric 
acid  on  indigo  contains  at  least  two  acid  compounds.     The  solu- 
tion is,  however,  commonly  spoken  of  as  sulphindigotic  acid, 
and  is  used  just  as  made,  or  partially  neutralized  with  sodium  or 
potassium  carbonate,  in  dyeing  the  color  known  as  Saxon  blue, 
and  in  the  preparation  of  various  sorts  of  bluing. 

342.  When  blue  indigo  is  treated  with  reducing  agents,  it  is 
converted  into  a  colorless  compound  soluble  in  alkaline  liquids 
and  known  as  "white  indigo."     On  exposure  to  the  air,  the 
white  indigo  is  reconverted  into  insoluble  indigo-blue. 

Exp.  159.  —  Into  a  test-tube  put  as  much  finely  powdered  indigo 
as  can  be  taken  on  the  point  of  a  small  penknife,  and  half  a  tea- 
spoonful  of  fine  zinc  filings  (zinc  dust  is  best  if  it  can  be  obtained). 
Pour  into  the  test-tube  two  teaspoonfuls  of  a  moderately  strong  solu- 
tion of  caustic  soda  and  heat  the  mixture  :  the  caustic  soda  acts  upon 
the  zinc  and  hydrogen  is  set  free  :  by  the  action  of  the  nascent  hydro- 


200  PHYSIOLOGICAL  CHEMISTRY*  [§  343. 

gen  the  indigo-blue  is  converted  into  white  indigo,  and  the  white 
indigo  dissolves  in  the  alkaline  liquid,  forming  a  yellowish  solution. 

The  formula  of  white  indigo  is  CieHisNsOs-  When  an  alkaline 
solution  of  white  indigo  is  exposed  to  the  air,  it  is  converted  into  indigo- 
blue  :— CisHiaNsOa  +  O  =  CieHioNsOg  +  H2O. 

Exp.  160.  —  Pour  out  a  portion  of  the  solution  of  the  preceding 
experiment  into  a  shallow  dish  and  observe  that  in  contact  with  the 
oxygen  of  the  air  insoluble  indigo-blue  is  formed. 

Exp.  161.  —  Dip  a  piece  of  white  cloth  or  filter  paper  into  the 
liquid  remaining  in  the  test-tube.  As  soon  as  the  moistened  cloth  or 
paper  conies  out  into  the  air  it  will  turn  blue. 

The  experiment  illustrates  the  method  actually  employed  to  some 
extent  in  dyeing  with  indigo.  Other  reducing  agents  are  also  used 
(very  commonly  a  mixture  of  slaked  lime  and  copperas),  the  action 
of  which  will  be  better  understood  hereafter.  The  cloth  dipped  into 
the  solution  of  white  indigo  becomes  thoroughly  impregnated  with 
this  solution,  and  when  the  indigo-blue  is  formed,  it  is  formed  within 
and  among  the  fibres  of  the  cloth,  so  that  the  color  is  "  fast." 

343.  Physiological  Chemistry.  —  The  study  of  the  various 
fluids  and  solids  occurring  in  the  living  animal,  and  concerned 
in  the  processes  of  circulation,  respiration  and  digestion,  belongs 
more  particularly  to  that  branch  of  the  science  designated  as 
physiological  chemistry,  and  is  not  fitted  for  an  elementary 
manual. 

The  chemical  relations  of  the  substances  concerned  in  the 
vital  functions  are,  as  a  rule,  but  imperfectly  understood,  and 
many  of  the  substances  themselves  are  extremely  complex  ; 
thus  to  albumin  has  been  assigned  the  formula  C72H112N18SO22, 
but  such  formulae  are  to  be  regarded  only  as  rough  approxima- 
tions. Bodies  of  like  complexity  also  occur  in  vegetables, 
although  the  mass  of  the  plant  is  made  up,  as  we  have  seen,  of 
substances  comparatively  simple  in  composition.  The  more 
particular  study  of  the  chemical  phenomena  involved  in  the 
growth,  nutrition  and  decay  of  plants  belongs  to  agricultural 
chemistry. 

In  this  place,  brief  mention  will  be  made  of  a  few  of  the 
more  important  compounds  which  occur  in  animals  and  plants, 
and  which  have  not  as  yet  been  considered. 


§  346.]  ALBUMIN.  -  FIBRIN.  —  CA SEIN.  201 

344.  Albumin  occurs  abundantly  in  many  of  the  fluids  and 
soft  solids  of  the  animal  body.     It  is  most  familiar  as  the  white 
of  the  eggs  of  birds  ;  it  is  found  also  in  considerable  proportion 
in  the  blood,  although  blood-albumin  differs  in  some  of  its  char- 
acters from  egg-albumin.     The  most  striking  properties  of  albu- 
min are  its  solubility  in  water,  and  its  coagulation  by  heat  and 
other  agents  ;  these  properties  may  be  exhibited  with  fresh  white 
of  egg. 

Exp.  162.  —  Beat  or  whip  the  white  of  an  egg  to  destroy  the 
transparent  membrane  of  the  cells  in  which  the  albumin  is  held,  and 
agitate  a  portion  with  water  :  it  dissolves  readily. 

Exp.  163.  —  Add  strong  alcohol  to  a  portion  of  the  solution  ob- 
tained in  Exp.  162.  The  albumin  is  coagulated. 

Exp.  164.  —  Place  a  little  of  the  albumin  in  a  test-tube,  put  the 
tube  into  water,  contained  in  a  beaker  or  evaporating-dish,  and  heat 
the  dish.  Observe  that  the  albumin  coagulates  some  time  before  the 
water  is  hot  enough  to  boil ;  namely,  at  about  60°. 

Albumin  is  a  very  complex  compound  of  carbon,  hydrogen  and 
oxygen,  and  contains  also  a  certain  proportion  of  nitrogen  and  sul- 
phur. A  body  of  similar  composition  occurs  in  vegetables,  and  is 
called  vegetable  albumin.  To  the  presence  of  sulphur  in  albumin,  and 
in  a  somewhat  similar  body  which  occurs  in  the  yolk  of  eggs,  is  due 
the  peculiar  odor  of  rotten  eggs  ;  to  the  same  presence  is  owing  the 
fact,  that  silver  spoons  used  in  eating  eggs  are  stained,  silver  sulphide 
being  formed. 

345.  Fibrin  occurs  in  the  animal  body  in  a  soluble  and  in 
an  insoluble  state.     In  the  soluble  state  it  occurs  in  the  blood ; 
but  when  exposed  to  the  air  this  fibrin  coagulates  and  forms  the 
clot.     By  washing  the  clot  with  water,  a  white,  stringy  mass  of 
fibrin  is  obtained.     In  the  insoluble  state  it  forms  the  fibres  of 
muscle ;  it  may  be  obtained  by  washing  a  piece  of  lean  meat 
repeatedly  until  the  coloring  matter  is  removed.     In  composi- 
tion fibrin  approaches  albumin,  but  contains  more  oxygen  and 
nitrogen  than  albumin.     A  similar  body  called  vegetable  fibrin 
occurs  in.  gluten. 

346.  Casein  occurs  in  the  milk  of  animals.     It  bears  some 
resemblance  to  albumin,  but  is  not  coagulated  by  heat.     It  is 
coagulated  by  acids   and  by  rennet,  the  inner  membrane   of 


202  GELATIN  AND   GLUE.  [§  347. 

the  stomach  of  the  calf.  Advantage  is  taken  of  this  fact  in 
the  manufacture  of  cheese,  which  is  made  by  warming  the 
milk  in  contact  with  rennet ;  the  casein  is  coagulated  and 
rises  to  the  surface  carrying  with  it  the  fatty  matters  held 
suspended  in  the  milk.  The  curd  thus  obtained  when  pressed 
is  cheese. 

347.  Milk    consist?    mainly    of   water   holding    in    solution 
casein,  milk-sugar  and  certain  salts,  such  as  sodium  and  potas- 
sium chlorides,  and  the  phosphates  of  calcium,  magnesium  and 
the  alkaline  metals.     It  holds  in  suspension  a  number  of  oily 
globules,  and  when  allowed  to  stand  quietly  these  globules  rise 
to  the  surface,  forming  the  cream.     The  residue,  after  the  removal 
of  the   cream  and  the  coagulation  of  the   casein,   is  the  whey. 
Butter  is  made  by  agitating  the  cream,  so  as  to  break  up  the 
little  globules  of  oily  matter,  and  allow  it  to  collect  together  in 
one  mass. 

Exp.  165.  —  Allow  some  fresh  milk  to  stand  until  the  cream  has 
risen  to  the  surface.  Remove  the  cream  by  skimming,  and  to  the 
skimmed  milk  add  a  little  dilute  sulphuric  acid.  The  milk  is  curdled, 
that  is,  the  casein  is  coagulated  and  rises  to  the  surface. 

348.  Legumin    is  a  substance  which   resembles   casein ;    it 
occurs  in  peas,  beans,  etc.     The  Chinese  make  a  sort  of  vege- 
table cheese  from  peas. 

349.  Gelatin  and  Glue.  —  Gelatin  is  a  body  consisting  of 
the  same  elements  as  albumin,  but  in  somewhat  different  propor- 
tions.    Gelatin  is  obtained  when  the  bones  or  skins  of  animals 
are  boiled  in  water.     It  is  soluble  in  boiling  water,  but  the  solu- 
tion gelatinizes  on  cooling.     Glue  is  an  inferior  variety  of  gela- 
tin, made  from  the  parings  and  refuse  of  ox-hides.     Isinglass  is 
made  from  the  swimming-bladder  of  sturgeons  and  other  fishes, 
and  is  nearly  pure  gelatin. 

Gelatin  does  not  occur  ready  formed  in  the  bones,  skin,  etc. 
but  is  produced  by  the  action  of  boiling  water  on  a  substance 
so  contained.  This  substance  is  called  ossein ;  a  somewhat 
similar  substance,  which  occurs  in  the  shells  of  lobsters  and 
crabs,  and  in  the  skins  of  earthworms,  is  called  chitUL 


$  351  1  DECAY  OF  ORGANIC  SUBSTANCES.  203 

y         *j  , 

Exp.  166.  —  Immerse  a  clean  bone  in  dilute  chlorhydric  acid 
(made  by  diluting  the  commercial  acid  with  six  times  its  bulk  of 
water).  The  mineral  part  of  the  bone  will  gradually  dissolve  away, 
and  after  three  or  four  days  there  will  be  left  a  flexible  substance 
which  preserves  the  shape  of  the  bone,  and  when  dry  has  a  translu- 
cent, horny  appearance.  This  is  ossein. 

Exp.  167.  —  Boil  the  ossein  of  Exp.  166  with  water  for  several 
hours.  It  dissolves  almost  entirely,  being  converted  into  gelatin. 
Allow  the  solution  to  cool  ;  it  will  gelatinize. 

350.  Decay  of  Organic  Substances,  —  Organic  substances, 
partly  on  account  of  the  complexity  of  their  structure,  are  very 
liable  to  undergo  change.     This  is  especially  true  of  substances, 
which  are  the  immediate  product  of  animal  or  vegetable  life. 
The    ultimate    or   final   products    of    the    decay    of    animal    or 
vegetable   matter   are   mainly   carbonic   acid   and   water,   since 
the  greater  part   of  all  organic  matter  is  made  up  of  carbon 
and  hydrogen  (and  oxygen).     This  complete   conversion  takes 
place  when  the  substances  are  exposed  to  a  high  temperature 
with   free   access   of    oxygen.      In   the    ordinary   processes   of 
decay,   however,   a   vast   variety  of  intermediate   products   are 
formed,    some    of    which   are   very   offensive,    especially   when 
sulphur  is  an  ingredient  of  the  decaying  substance.     By  the 
decay  of    substances    containing   nitrogen  ammonia  is  formed, 
and,  under  certain  conditions,  nitric  acid:  nitrates  are  always 
found  in  the  soil  and  in  well  waters  of  thickly  inhabited  locali- 
ties, and  calcium  nitrate  is  made  artificially  by  allowing  nitro- 
genous organic  matter,  mixed  with  lime  or  plaster,  to   decay 
slowly  in  the  air. 

351.  The   intermediate    products    of    the    decay   of   organic 
substances  are  as  a  rule  imperfectly  known  :  certain  forms  of 
decay,  such  as  the  various  sorts  of  fermentation,  have  been 
carefully  studied,  but  in  other  cases,  as  in  the  slow  decay  of 
woody  fibre  in  the  soil,  little  is  known  with  certainty  on  ac- 
count of  the  difficulty  of  isolating  the  various  compounds  in  a 
state  of  assured  purity.     Even  in  the  case,  however,  of  simple 
fermentation   of   grape-sugar,   the  chemical  changes  are  by  no 
means  as  simple  as  might  at  first  appear  from  Exp.  100,  §  226. 


204   .  PRESERVATIVE  AGENTS.  [§  35 2. 

Although  the  reaction  of  §  193,  which  represents  the  conver- 
sion of  the  sugar  into  carbonic  acid  and  alcohol,  expresses  the 
main  reaction  which  occurs,  yet,  in  addition  to  these  products, 
there  are  formed  several  other  bodies  in  greater  or  less  amount  ; 
thus  lactic  and  succinic  acids,  glycerin  and  a  brown  substance 
resembling  caramel  are  among  the-  usual  products  of  alcoholic 
fermentation. 

352.  The  natural  decay  to  which  dead  organized  bodies  are 
prone  may  be  arrested  more  or  less  completely  by  the  use  of 
certain  chemical  agents,  or  in  some  cases  by  the  simple,  exclu- 
sion of  air.  Warmth  and  moisture  are  among  the  conditions 
favorable  for  the  beginning  of  decomposition ;  in  a  cold  climate 
or  in  winter,  animal  substances  may  be  kept  for  a  much  longer 
period  than  in  summer. 

Among  the  chemical  substances  used  as  antiseptic  or  pre- 
servative agents  are  common  salt,  which  is  used  in  the  curing 
of  meat  and  fish  ;  wood-smoke,  which  owes  its  virtue  to  the 
kreasote  (§  282)  contained  in  it,  and  which  is  used  in  the  smok- 
ing of  hams  and  other  articles  of  food ;  kreasote  itself  and  car- 
bolic acid,  the  use  of  which  was  illustrated  in  Exp,  128 ;  and 
the  dead  oil  of  tar  (§  275),  used  in  preserving  timber.  The 
effect  of  the  exclusion  of  air  is  illustrated  in  the  canning  of 
fruits  ;  also  by  the  domestic  processes  of  "  preserving "  fruits 
by  immersion  in  strong  sirup. 


CHAPTEK  XVIII. 

SILICON  AND  BORON. 

SILICON    (Si). 

353.    After  oxygen,  silicon  is  the  most  abundant  and  widely 
diffused  of  all  the  chemical  elements.     It  occurs  in  combination 


§  356.]  SILICA   AND  SILICATES.  205 

with  oxygen  as  silica  and  in  combination  with  oxygen  and 
various  metallic  elements  as  silicates  of  those  elements. 

354.  Silicic  anhydride  or  Silica  (SiO2)  occurs  in  nature  as 
quartz,  flint,  rock-crystal,  agate,  etc.     It  occurs  also  in  plants, 
particularly  in  the  outer  covering  of  the  stalks  and  the  husks 
of  grain.     The  cuticle  of  rattan,  for  example,  contains  a  large 
proportion  of  silica,  and  the  same  remark  is  true  of  most  of  the 
grasses  and  grains.      The  value  of  the  plant  called  horse-tail 
(Equisetum)  as  a  polishing  or  scouring  agent  depends  upon  the 
large  quantity  of  silica  contained  in  it. 

355.  As  it  occurs  in  nature,  silica  is  insoluble  in  water,  but 
dissolves  with  more  or  less  difficulty  in  caustic  soda  (or  potash), 
forming  sodium   (or  potassium)   silicate.      The   potassium   and 
sodium  silicates  are  used  in  the  arts  under  the  name  of  water- 
glass  or  soluble  glass. 

Exp.  168.  —  To  a  concentrated  solution  of  water-glass  contained 
in  a  small  evaporating-dish,  add  enough  strong  chlorhydric  acid  to 
make  the  solution  acid.  There  will  separate  a  thick  jelly-like  mass 
of  silicic  acid  (H4SiO4).  Evaporate  the  contents  of  the  dish  to  dry- 
ness  on  a  water-bath,  and  then  heat  the  residue  gently  over  the  gas- 
lamp.  The  mass  will  contract  in  bulk,  and,  on  adding  water,  there 
will  remain  undissolved  a  fine  white  powder  of  silicic  anhydride. 

Exp.  169.  —  Take  a  very  dilute  solution  of  water-glass,  and  add 
dilute  chlorhydric  acid  drop  by  drop  until  the  liquid  has  a  decidedly 
acid  reaction.  No  precipitation  will  occur  :  the  silicic  acid  which  is 
set  free,  as  in  the  preceding  experiment,  remains  dissolved  in  the  acid 
liquid. 

It  is  possible,  also,  to  prepare  an  aqueous  solution  of  silicic  acid, 
but  if  these  solutions  be  evaporated  to  dryness  and  the  residues 
heated,  there  is  formed  in  each  case  the  insoluble  silicic  anhydride. 

356.  Silicates.  —  Silicic    anhydride    combines   with    many 
of  the  metallic  oxides  to   form   silicates.      Hundreds  of  sili- 
cates  occur  in  nature  as  crystallized   minerals  ;  thus  ordinary 
feldspar  is  a  double  silicate  of  aluminum  and  potassium,  com- 
mon mica  is  a  complex  silicate  of  aluminum,  iron  and  potas- 
sium. 

18 


206  GLASS.  [§  357. 

357.  Glass.  —  Besides  the  silicates  which  occur  in  nature, 
there  are  artificial  silicates  of  great  importance  in  the  arts  and 
in   every-day   life.      Sodium   silicate    (water-glass),    which   has 
already  been  alluded  to,  is  extensively  used  by  calico-printers 
and  soap-makers.     Its  chief  use,  however,  is  as  a  component 
of  common  glass.     The  various  glasses  of  commerce  are  mix- 
tures of  a  highly  silicious  silicate  of  sodium,  or  of  potassium, 
or  of  both  these  substances,  with  silicates  of  other  metals,  such 
as  calcium,  aluminum  and  lead.     The  silicates  of  the  alkaline 
metals  are  non-crystalline  and  soluble  in  water,  the  silicates  of 
most  of  the  other  metals  have  a  tendency  to  assume  the  crys- 
talline form.     It  has  been  found  that,  by  combining  the  alka- 
line silicates  with  the  silicates  of  certain  other  metals,  such  as 
calcium,  there  may  be  obtained  compound  glasses  which,  while 
they  retain  the  amorphous  character  of  the  alkaline  silicates, 
are  capable  of  resisting  the  action  not  only  of  air  and  water, 
but  even  of  acids  and  alkalies,  to  a  very  great  extent ;  thus, 
ordinary,  window-glass  is  composed  of  silicates  of  sodium  and 
calcium ;  Bohemian  glass,  suitable  for  ignition-tubes,  consists  of 
silicates  of  potassium  and  calcium  ;  flint-glass  contains  silicates 
of  potassium  and  lead.     Bottle-glass  is  a  mixture  of  silicates  of 
calcium,  aluminum,  iron  and  sodium.     The  silicates  of  some  of 
the  metals  are  colored  :  the  green  color  of  bottle-glass  is  due  to 
the  presence  of  ferrous  silicate ;  cobalt  silicate  gives  a  beautiful 
blue,  manganese  silicate  a  violet  and  uranium  silicate  a  yellow 
color  to  the  glass. 

358.  Silica  and  the  silicates  are  readily  attacked  by  fluor- 
hydric    acid,    as    has    been    already   seen   (Exp.   41,    §  100). 
When  silica  is  treated  with  dry  fluorhydric  acid  gas,  there  is 
formed  a  gaseous  compound  known  as  silicon  fluoride  (SiF4) 
which,  in  contact  with  water,  decomposes  into  gelatinous  sili- 
cic  acid,  and   another   compound   known   as   fluo-silicic   acid 
(2HF,SiF4):- 

3  SiF4  +  4  H20  =  SiH404  -f  2  (2  HF,SiF4) 

Exp.  170.  —  Into  a  perfectly  dry  tube  of  hard  glass,  No.  5,  closed 
at  one  end,  drop  a  small  quantity  (as  much  as  can  be  taken  on  the 


§  361,] 


SILICON. —BORON. 


207 


Fig.  63. 


point  of  a  penknife)  of  a  mixture   of  equal  parts   of  .fine  quartz 

sand    and    powdered    fluor-spar    (calcium    fluoride).      Moisten    the 

mass  with   a  drop   of  strong  sulphuric   acid,  and 

heat  in  the  flame   of  the   lamp.     Gaseous   silicon 

fluoride  will  escape  from  the  tube,  and  if  a  drop  of 

water  in  the  loop  of  a  bit  of  platinum  wire,  or  on  a 

colored  glass  rod,  be  held  at  the  mouth  of  the  tube, 

the  water  will  become  cloudy  from  the  deposition 

of  silicic  acid. 

359.  Silicon  (Si)  may  be  obtained  pure  from 
a  compound  known    as  potassium   fluo-silicate. 
Three   allotropic   conditions   are    known    cor- 
responding to  the  three  modifications  of  carbon 
(§  174).     The   amorphous   variety   is  a   brown 
powder  which  burns  readily  in  air  or  oxygen, 
forming   silicic  anhydride  (SiO2).     The  atomic 
weight  of  silicon  is  28. 

360.  Silicon  in   Organic   Compounds.  —  The  most  impor- 
tant of  the  organic  compounds  containing  silicon  are  the  so- 
called    silicic   ethers   or   the  silicates  of   the  organic  radicals  ; 
thus  methyl  silicic  ether  is  (CH3)4SiO4 ;  ethyl  silicic  ether  is 
(C2H5)4SiO4,  etc.     These  are  all  artificial  bodies  ;  they  are  vola- 
tile, colorless,  inflammable  liquids  having  generally  an  ethereal 
odor. 

BORON  (B). 

361.  Boron  is  found  in  nature  in  combination  with  oxygen, 
as  boracic    acid,   and  in  combination  with   oxygen  and   some 
metallic  element,  the  most  important  compound  being  sodium 
biborate,  commonly  called  borax. 

In  certain  volcanic  districts  in  Tuscany,  jets  of  steam  mixed  with 
other  vapors  escape  continually  from  cracks  in  the  soil,  and  bring  to 
the  surface  small  quantities  of  boracic  acid.  Since  boracic  acid  is 
not  volatile,  in  the  ordinary  sense  of  the  term,  at  temperatures  as  low 
as  100°,  it  appears  that  it  is  transported  mechanically  by  the  steam, 
much  in  the  same  way  that  dust  is  carried  along  by  a  current  of  air. 
The  jets  of  vapor,  laden  with  boracic  acid,  are  made  to  bubble 
through  water  as  they  escape  from  the  earth,  and  the  solution  thus 


208  BORACIC  ACID.  [§  362. 

obtained  is  evaporated  in  pans,  beneath  which  hot  currents  of  vapor 
from  the  earth  are  caused  to  circulate,  until  it  is  concentrated  to  such 
a  point  that  on  cooling  the  boracic  acid  crystallizes  out. 

.  362.  Boron  (B).  —  Of  boron  itself  little  need  be  said.  It 
resembles  carbon  in  that  it  may  be  obtained  in  an  amorphous 
condition  like  charcoal,  and  also  crystallized  like  the  diamond. 
The  atomic  weight  of  boron  is  11. 

363.  Boracic  acid  (H3BO3)  is  but  a  feeble  acid  at  ordinary 
temperatures  ;  it  may  be  set  free  by  treating  any  borate  with 
almost  any  acid,  excepting  carbonic  acid. 

Exp.  171.  —  Dissolve  4  grms.  of  powdered  borax  in  10  grms.  of 
boiling  water,  in  a  beaker-glass  or  porcelain  capsule  of  30  or  40  c.  c. 
capacity,  and  add  to  the  solution  2.5  grms.  of  concentrated  chlor- 
hydric  acid.  As  the  solution  cools,  boracic  acid  will  be  deposited  in 
the  form  of  glistening,  colorless  plates  or  scales. 

364.  Boracic  acid  imparts  to  the  flame  of  burning  alcohol 
a  peculiar  green  tint,  which  is  quite  characteristic,  and  affords 
a  valuable   test   by   which  the  presence  of   the  acid  may  be 
detected. 

Exp.  172.  —  Dissolve  a  little  crystallized  boracic  acid  in  a  tea- 
spoonful  of  alcohol  in  a  small  porcelain  capsule.  Set  fire  to  the 
alcohol  and  stir  the  burning  solution  with  a  rod,  or  agitate  it  by  jarring 
the  dish.  The  flame  of  the  alcohol  will  be  of  a  fine  green  color. 

365.  Boracic  anhydride  (B2O3)  may  be  prepared  by  heating 
crystallized  boracic  acid,  as  follows. 

Exp.  173. — In  a  clean  iron  spoon  heat  some  crystallized  boracic 
acid.  The  crystals  will  melt,  and  if  the  heat  be  continued,  the 
mass  will  become  pasty,  and  will  swell  up  as  the  water  is  expelled. 
After  all  the  water  has  been  driven  off  by  strong  heat,  the  anhydride 
is  left  as  a  clear,  viscous  liquid,  from  which  long  threads  may  be 
drawn  out  by  touching  to  the  surface  of  the  liquid  the  end  of  a  stick 
or  glass  rod,  and  then  gently  pulling  away  the  stick  with  the  matter 
which  has  adhered  to  it. 

If  the  fused  mass  be  allowed  to  cool,  it  will  solidify  to  a  hard, 
transparent  glass,  which  soon  cracks  in  every  direction  and  splits  up 
into  fragments. 


§  367.]  SODIUM.  — COMMON  SALT.  209 

CHAPTER  XIX. 
SODIUM  (Na). 

366.  This  abundant  element  is  chiefly  found  in  nature  in 
the   state    of    chloride,   nitrate,   carbonate,   borate   and  silicate. 
The  most  abundant  of  its  compounds  is  common  salt,  which 
is  the  combination  of  sodium  with  chlorine  (NaCl).     On  ac- 
count of   the   inexhaustible  abundance  of   common    salt,    this 
substance  constitutes  the  chief   source  from  which  all  manu- 
factured compounds   of    sodium  are  more  or  less  directly  de- 
rived ;  one  other  natural  sodium-containing  mineral,  however, 
deserves    mention   as   a   source    of    sodium   compounds,  —  the 
mineral  cryolite,  —  a  double   fluoride  of   sodium   and   alumi- 
num (§  98). 

367.  Sodium  Chloride  or  Common  Salt  (NaCl).  —  This  natu- 
ral mineral  ib,  when  pure,  a  colorless,  transparent,  anhydrous 
stone,   which  crystallizes   in    cubes,  dissolves  readily  in  about 
three  times  its  weight  of  cold  water,  and  possesses  a  specific 
gravity  of  2.15,  and  an  agreeable  taste,  which,  because  familiar, 
is  the  representative  or  type  of  that  peculiar  savor  called  saline. 
A  saline  taste  means  a  taste  suggestive  of  that  of  common  salt, 
just   as  the  phrase,  "  saline  substance,"  characterizes  a  very 
large  class  of  bodies  which  resemble  more  or  less  in  appearance 
and  properties  the  longest  and  best  known  of  all  such  substan- 
ces, —  common  salt. 

There  are  three  sources  of  salt,  —  the  beds  of  the  native  min- 
eral, saline  springs  and  sea-water.  In  all  cases  in  which  the  salt  is 
obtained  from  its  solution  in  water,  evaporation  by  fire,  or  by  the 
heat  of  the  sun  in  warm,  sunny  climates,  is  necessary.  When  pure 
enough,  the  rock-salt  is  mined  like  any  other  ore,  but  when  it  is 
mixed  with  earth  or  other  impurities,  as  it  lies  in  its  natural  bed,  the 
solubility  of  the  sodium  chloride  in  water  is  availed  of  to  free  the 
salt  from  its  insoluble  impurities,  and  to  facilitate  the  lifting  of  it  to 
the  surface  of  the  earth.  Water  is  let  in  to  the  bed  of  salt,  and 
allowed  to  remain  there  till  it  has  become  saturated  ;  the  brine  is 
18* 


210  MANUFACTURE  OF  SALT.  [§368. 

then  pumped  out  and  evaporated.  Some  natural  brine-springs  contain 
so  small  a  proportion  of  salt  that  some  cheaper  mode  of  evaporation 
than  by  fire  is  essential  to  their  profitable  working.  Such  waters  are 
concentrated  by  a  process  termed  graduation.  The  brine  is  pumped 
up  to  a  sufficient  height,  and  then  allowed  to  trickle  slowly  over  large 
stacks  of  fagots,  which  are  sheltered  by  a  roof  from  rain,  but  are 
freely  exposed  to  the  prevailing  wind.  The  brine,  thus  diffused  over 
a  very  large  surface,  is  rapidly  concentrated  by  the  draught  of  air.  By 
repeating  the  process  a  moderate  number  of  times,  a  weak  brine  may 
be  brought  to  a  degree  of  concentration  at  which  evaporation  by  fire 
may  be  employed.  If  .the  strong  brine  is  boiled  down  rapidly,  a  fine- 
grained table-salt  is  obtained  ;  if  it  is  slowly  evaporated,  a  hard, 
coarsely  crystallized  salt  is  the  product.  The  thick  mother-liquor, 
from  which  no  more  sodium  chloride  will  crystallize,  contains  the 
more  soluble  salts  of  the  original  brine,  such  as  calcium  chloride, 
magnesium  chloride  and  bromide,  besides  a  large  proportion  of  com- 
mon salt  which  cannot  be  separated  from  the  liquor.  Such  mother- 
liquors  are  sometimes  so  rich  in  magnesium  salts  as  to  be  advan- 
tageously worked  for  these  substances,  and  they  are  also  sometimes 
profitable  sources  of  bromine.  Considerable  quantities  of  magnesium 
salts  and  of  bromine  have  also  been  extracted  from  concentrated 
sea- water,  after  all  the  available  sodium  chloride  has  been  withdrawn. 
The  salt  of  commerce  generally  contains  a  small  proportion  of  mag- 
nesium chloride,  which  makes  it  slightly  deliquescent  and  bitter. 

Exp.  174.  —  Dissolve  9  grms.  of  fine  salt  in  25  c.  c.  of  water  at 
the  ordinary  temperature.  Add  to  the  solution  another  gramme  of 
salt  ;  it  will  not  dissolve.  Bring  the  solution  to  boiling ;  the  added 
gramme  of  salt  will  barely  dissolve.  Sodium  chloride  is  scarcely  more 
soluble  in  hot  than  in  cold  water,  wherein  it  differs  from  the  great 
majority  of  soluble  salts.  Evaporated  brines  deposit  their  salt  with 
almost  equal  facility  when  hot  and  when  cold,  but  the  hot  liquors  will 
hold  in  solution  a  much  greater  proportion  of  the  salts  with  which 
the  sodium  chloride  is  associated,  than  the  cold  brines  could  retain. 
In  the  process  of  evaporation  by  fire,  the  associated  magnesium,  cal- 
cium and  sodium  salts  do  not,  therefore,  crystallize  with  the  common 
salt,  but  remain  in  the  hot  mother-liquor. 

368.  The  uses  of  common  salt  are  manifold  ;  since  it  is  a  con- 
stituent of  almost  all  kinds  of  food,  and  essential  to  the  life  of 
animals,  it  is  not  surprising  that  salt  exists  in  small  quantities 
in  almost  every  spring,  soil,  plant  and  animal.  The  antiseptic 


369.] 


SODIUM  SULPHATE. 


Duality  of  salt  is  applied  to  the  preservation  of  fish,  meat  and 
wood.  Salt  is  extensively  employed  in  glazing  earthen-ware,  its 
volatility  at  furnace-heat  combining  with  other  qualities  to  fit  it 
for  this  use.  Immense  quantities  of  salt  are  consumed  in  pre- 
paring sodium  sulphate,  from  which  in  turn  common  "  soda  " 
(sodium  carbonate)  is  made.  Salt  is  also  the  source  from  which 
chlorhydric  acid  is  derived  (§  72). 

369.  Sodium  sulphate  (Na2SO4)  is  made  in  great  quantities 
from  common  salt  and  sulphuric  acid  as  a  preliminary  step  in  the 
manufacture  of  sodium  carbonate. 

The  process  has  two  stages.  The  mixture  of  salt  and  sulphuric 
acid  is  first  heated  in  large,  covered  cast-iron  pans.  As  in  Exp.  28, 
chlorhydric  acid  is  disengaged  from  the  mixture,  and  is  absorbed  by 
being  passed  through  vertical  stone  towers  filled  with  lumps  of  coke, 
over  which  water  is  kept  trickling.  The  reaction  which  takes  place 
in  the  iron  pans  is  not  complete,  a  portion  of  the  sodium  chloride 
remaining  undecomposed.  The  reaction  at  this  first  stage  may  be 
represented  as  follows  :  — 

2  NaCl  -f-  H2S04  =  NaCl  -f  HNaSO4  -f  HC1. 

The  pasty  mass  is  then  pushed  into  an  adjoining  fire-brick  chamber, 
which  is  strongly  heated  by  flues  from  a  furnace.  The  hydrogen 
sodium  sulphate,  of  the  last  reaction,  decomposes  the  remainder  of 
the  salt,  and  a  further  quantity  of  chlorhydric  acid  is  disengaged  to 
be  condensed  by  the  water  in  the  coke-towers,  while  sodium  sul- 
phate remains  :  — 

NaCl  -f  HNaS04  =  Na2SO4  -f  HC1. 

The  sodium  sulphate,  resulting  from  this  process,  is  a  white, 
anhydrous  salt,  which  dissolves  easily  in  water  at  30°.  When  a 
strong  solution  of  the  anhydrous  salt,  made  at  this  temperature, 
is  cooled,  there  separate  large,  colorless  crystals  of  a  transparent 
salt,  bitter  and  cooling  to  the  taste.  This  salt,  long  known  as 
Glauber's  salt,  contains,  besides  the  elements  of  sodium  sul- 
phate, ten  molecules  of  water  ;  it  therefore  answers  to  the 
formula,  Na2SO4,10  H2O.  The  crystallized  salt  loses  water  on 
exposure  to  dry  air  ;  it  effloresces  and  is  converted  into  the 
anhydrous  salt. 


212  MANUFACTURE   OF  SODIUM  CARBONATE.       [§  370. 

Exp.  175.  —  Dissolve  10  grms.  of  crystallized  Glauber's  salt  iif" 
water,  the  temperature  of  which  has  been  previously  observed  ;  dur- 
ing solution,  the  temperature  falls,  —  cold  is  produced  in  consequence 
of  the  expenditure  of  some  of  the  heat  of  the  mixture  in  overcoming 
the  cohesion  of  the  crystallized  salt.  Dissolve  a  like  quantity  of 
effloresced  Glauber's  salt  (anhydrous  sodium  sulphate)  in  a  small 
bulk  of  water  ;  heat  will  be  developed.  A  part  of  the  water  is  solidi- 
fied by  combining  with  the  anhydrous  sulphate  to  form  the  hydrated 
sulphate,  and  the  heat,  which  before  kept  that  quantity  of  water  fluid, 
being  set  free  to  do  other  work,  raises  by  a  certain  amount  the  tem- 
perature of  the  mixture. 

370.  Sodium  Carbonate  (Na2CO3).  —  The  manufacture  of 
this  substance  constitutes  one  of  the  most  important  branches 
of  chemical  industry.  Immense  quantities  of  it  are  consumed 
in  the  fabrication  of  glass  and  soap,  in  the  preparation  of -the 
various  compounds  of  sodium,  and  in  washing,  both  by  the 
manufacturer  of  cloth  and  in  the  household.  The  ashes  of  sea 
and  sea-shore  plants  were  formerly  the  source  of  the  sodium 
carbonate,  but  it  is  now  chiefly  made  from  common  salt  by  a 
process  called,  from  the  name  of  its  French  inventor,  Leblanc's 
process. 

The  first  stage  of  this  process  we  have  already  studied  ;  it  consists 
in  the  preparation  of  the  sodium  sulphate  from  common  salt.  In  the 
second  stage,  the  sodium  sulphate  is  mixed  with  coal  and  chalk,  or 
limestone  (calcium  carbonate),  and  heated  in  a  reverberatory  furnace. 
The  carbon  of  the  coal  takes  oxygen  from  the  sodium  sulphate 
(Na^SO^,  and  would  leave  sodium  sulphide  (Na.,S)  ;  but,  at  the 
same  time,  an  interchange  takes  place  between  the  sodium  sulphide 
and  the  calcium  carbonate,  forming  sodium  carbonate  and  calcium 
sulphide.  The  mass  remaining  after  the  reaction  is  complete  is  called 
"  black  ball "  or  "  black  ash."  When  cold  it  is  systematically  washed 
with  warm  water  until  all  the  soluble  portions  are  extracted.  The 
solution  is  evaporated  in  large  iron  pans  by  the  waste  heat  of  the  re- 
verberatory furnaces,  and  again  calcined.  The  product  of  this  heat- 
ing is  the  soda-ash  of  commerce  ;  it  is  almost  white,  and  generally 
contains  about  80  per  cent  of  pure  anhydrous  sodium  carbonate.  As 
some  caustic  soda  is  always  contained  in  the  black-ash,  the  solution  is 
frequently  concentrated  until  the  carbonate  crystallizes  out,  and  the 
mother-liquor  is  used  for  the  manufacture  of  caustic  soda. 


§  37i.; 


REVERBERATORY  FURNACE. 


213 


Fig.  64  represents  a  reverberatory  furnace  such  as  is  used  in  the 
manufacture  of  wrought  iron  :  the  furnaces  used  in  the  manufacture 
of  soda-ash  differ  in 
their  details  from 
the  one  figured,  but 
the  general  princi- 
ple is  the  same. 
In  a  reverberatory 
furnace  the  sub- 
stance to  be  heated 
does  not  come  into 
immediate  contact 
with  the  fuel ;  the 
fire  is  built  upon 
the  grate-bars  (G) 
and  the  flame  plays  over  the  hearth  (H),  the  heat  being  reflected 
downward  from  the  curved  roof. 

The  so-called  crystals  of  soda  are  obtained  by  dissolving  the  crude 
soda-ash  in  hot  water,  and  suffering  the  hot  solution  to  cool  in  large 
pans.  In  the  course  of  five  or  six  days,  large  transparent  crystals  are 
formed  which  contain  62.93  per  cent  of  water,  and  correspond  to  the 
formula  Na2CO3,10  H2O.  The  crystals  effloresce  in  the  air  ;  they 
have  a  disagreeable  taste,  called  alkaline,  are  soluble  in  very  large 
proportion  both  in  hot  and  cold  water,  and  even  melt  at  a  moderate 
temperature  in  their  own  water  of  crystallization.  The  crystals  read- 
ily part  with  all  their  water,  and  the  dry  residue  melts  at  a  bright 
red  heat ;  this  residue  is  anhydrous  sodium  carbonate,  purified  by  the 
process  of  crystallization  which  it  has  undergone.  In  this  case,  as 
in  all  others,  the  process  of  crystallization  consists  essentially  in  the 
aggregation  of  like  particles  ;  the  strong  tendency  is  to  exclude  hete- 
rogeneous particles,  or,  in  other  words,  impurities,  from  the  crystalliz- 
ing structure.  There  is  no  more  universally  applicable  and  valuable 
means  of  purification  than  the  process  of  crystallization. 

371.  Hydrogen  Sodium  Carbonate  (HNaCO3). — When 
masses  of  crystals  of  hydrated  sodium  carbonate  (soda  crystals) 
are  exposed  to  an  atmosphere  of  carbonic  acid  gas,  they  absorb 
carbonic  acid  with  an  evolution  of  heat  sufficient  to  expel  the 
greater  part  of  their  water  of  crystallization.  A  white  powder 
remains  whose  formula  is  HNaCO, ;  the  dualistic  formula 


214  PROPERTIES  OF  SODIUM.  [§  372. 

(§  153)  is  Na2O,H2O,2  CO2,  whence  its  most  familiar  name, 
—  bicarbonate  of  soda.  This  substance  is  one  of  the  ingre- 
dients in  most  of  the  artificial  yeasts  used  for  raising  bread, 
cake  and  puddings,  and  is  known  to  grocers  and  cooks  as  "  soda,1' 
although  the  constituent  which  is  really  utilized  is  the  carbonic 
acid. 

,  From  sodium  bicarbonate,  carbonic  acid  may  be  set  free  by  almost 
,any  acid  or  acid  salt.  "  Rochelle  powders "  consist  of  sodium 
bicarbonate  in  one  paper  and  cream  of  tartar  in  another  ;  when  these 
two  materials  are  mixed  in  water,  carbonic  acid  is  set  free,  and  a 
double  tartrate  of  sodium  and  potassium,  called  Rochelle  salt, 
and  used  as  a  purgative,  remains  in  the  liquid  (see  §  328).  When 
bread  or  cake  is  "raised"  with  "soda"  and  cream  of  tartar,  the 
escaping  carbonic  acid  is  the  agent  in  puffing  up  the  dough,  and  the 
same  Rochelle  salt  remains  in  the  bread.  Tartaric  acid  and  cream 
of  tartar  having  been  dear  in  late  years,  a  cheaper  chemical  yeast 
powder  has  been  made  from  acid  calcium  phosphate  ;  when  this 
substance  reacts  within  the  dough  with  sodium  bicarbonate,  there 
remains  in  the  bread  a  mixture  of  the  phosphates  of  sodium  and  cal- 
cium. Alum  is  sometimes  used  for  the  same  purpose.  It  is  necessary 
to  employ  for  such  purposes,  in  connection  with  the  bicarbonate,  acids 
or  acid  salts  which  are  solid,  and  not  so  corrosive  as  to  be  obviously 
dangerous  and  harmful. 

372.  Sodium  (Na).  —  The  element  sodium  is  never  found 
uncombined  in  nature,  for  the  reason  that  in  its  elementary  con- 
dition it  cannot  exist  in  contact  with  either  air  or  water.  It 
is,  however,  artificially  prepared  from  sodium  carbonate  without 
serious  difficulty,  and  it  might  be  produced  in  considerable  quan- 
tities if  there  were  any  large  use  for  the  element.  The  atomic 
weight  of  sodium  is  23. 

The  properties  of  the  element  sodium  are  very  curious.  The 
substance,  when  freshly  cut,  or  when  melted  under  naphtha  or 
in  an  atmosphere  artificially  deprived  of  oxygen,  has  the  bril- 
liant, white,  metallic  lustre  of  silver.  Though  possessing  so 
eminently  this  characteristic  property  of  the  class  of  bodies 
called  metals,  and  being  like  them  a  good  conductor  of  heat  and 
electricity,  sodium  is  far  from  resembling  the  ordinary  metals  in 
other  respects  ;  thus  it  is  lighter  than  water,  having  a  specific 


§  373.]  SODIUM  DECOMPOSES   WATER.  215 

gravity  of  only  0.972,  whereas  the  common  metals  are  dense  and 
heavy  ;  again,  it  is  as  soft  as  wax  at  common  temperatures,  and 
melts  at  a  temperature  below  that  of  boiling  water  ;  while  it  has 
none  of  the  comparative  permanence  which  characterizes  lead, 
tin,  copper,  silver,  gold  and  other  familiar  metals.  If  exposed 
to  the  air,  even  for  a  few  seconds  only,  it  tarnishes,  and  soon 
becomes  covered  with  a  coating  of  oxide.  Hence  the  necessity 
of  preserving  the  metal  under  some  liquid  which,  like  naphtha, 
contains  no  oxygen.  We  have  already  seen  that  it  decomposes 
cold  water  (Exp,  8),  setting  free  its  hydrogen,  and  combining 
with  its  oxygen. 

Exp.  176.  —  Cover  the  bottom  of  a  large  bottle  (at  least  a  litre- 
bottle)  with  hot  water,  drop  in  a  piece  of  sodium  as  large  as  a  small 
pea,  and  immediately  cover  the  mouth  of  the  bottle  with  a  card  or 
glass  plate.  The  heat  caused  by  the  chemical  combination  of  the 
sodium  and  the  oxygen  of  the  water  is  sufficient  to  inflame  the  hydro- 
gen set  free ;  the  escaping  hydrogen  carries  with  it  a  small  ™  6_ 
portion  of  the  volatilized  sodium,  and  therefore  burns  with 
an  intensely  yellow  flame  which  is  very  characteristic  of 
sodium  compounds.  The  metal  swims  rapidly  about  on 
the  surface  of  the  water,  and  is  completely  converted  into 
caustic  soda  ;  at  a  little  interval,  after  the  flame  has  ceased 
to  burn,  a  globule  of  caustic  soda,  which  has  escaped  solu- 
tion, bursts  and  scatters  in  all  directions  ;  the  mouth  of  the 
bottle  should  always  be  covered  to  avoid  the  possible  pro- 
jection of  particles  of  hot  soda  out  of  the  bottle.  The  water  in  the 
bottle,  tested  with  litmus  paper,  will  be  found  to  possess  a  strong 
alkaline  reaction.  If  the  bit  of  sodium  be  previously  wrapped  up  in 
a  piece  of  cloth,  it  will  take  fire  in  cold  water  or  even  on  ice.  The 
cloth  prevents  the  sodium  from  moving  about,  and  the  heat  of  com- 
bination is  therefore  concentrated  upon  one  spot. 

373.  Sodium  Hydrate  (NaHO).  —  When  sodium  is  burnt 
upon  water,  a  solution  of  sodium  hydrate  possessing  an  intensely 
alkaline  reaction,  remains  behind  ;  but  the  hydrate  is,  in  prac- 
tice, made  from  the  carbonate.  The  sodium  carbonate  is  dis- 
solved in  boiling  water,  and  slaked  lime  mixed  with  water  to 
the  consistency  of  cream  is  run  into  the  hot  liquor.  The  cal- 
cium of  the  slaked  lime  replaces  the  sodium  in  the  sodium  car- 


21 6  SODIUM  HYDRATE.  -  SOAP. ...  [§  ,374, 

bonate  ;  a  white  insoluble  precipitate  of  calcium  carbonate  is 
formed,  and  sodium  hydrate  remains  in  the  solution  :  Na2CO8 
-\-  CaH2O2  =  2  NaHO  -j-  CaCOs.  The  solution  of  sodium  hy- 
drate after  separation  from  the  precipitate  of  calcium  carbonate 
is  evaporated  until  it  reaches  the  desired  strength.  The  evapora- 
tion may  be  continued,  until,  at  a  nearly  red  heat,  an  oily  liquid 
is  obtained  which  solidifies  on  cooling  to  a  white,  somewhat 
translucent  mass,  whose  composition  corresponds  to  the  formula 
NaHO.  It  is  very  soluble  in  water,  and  greedily  absorbs  both, 
water  and  carbcuic  acid  from  the  air. 

374.  Caustic  soda  is  manufactured  in  large  quantities  princi- 
pally for  the  use  of  the  soap-maker.     Soap,  as  we  have  already 
seen  (Exp.  Ill,  §  243),  is  made  by  boiling  together  grease  or  oil 
with  caustic  soda  or  potash  ;  soda-lye  yields  a  hard  soap,  potash- 
lye  a  soft  soap. 

The  cleansing  action  of  soap,  on  which  its  use  depends,  may  be 
explained  as  follows.  When  soap  is  dissolved  in  water  it  undergoes 
a  chemical  change;  regarding  the  soap  as  sodium  stearate,  we  may 
say  that  a  partial  interchange  takes  place  between  the  sodium  of  the 
soap  and  the  hydrogen  of  the  water,  and  there  is  formed  a  hydrogen 
sodium  stearate  and  a  certain  amount  of  caustic  soda.  The  caustic 
alkali  thus  set  free  attacks  the  greasy  and  oily  matters  of  the  article 
to  be  cleansed,  and  the  somewhat  sticky  solution  of  soap  holds  in 
suspension,  and  thus  removes  mechanically  the  particles  of  dust  and 
other  insoluble  matters. 

375.  Sodium  hydrate  is  an  example  of  the  class  of  bodies  called 
bases  (§61).     It  colors  litmus  blue  and  turmeric  brown,  and  when 
it  is  mixed  in  due  proportion  with  an  acid,  a  saline  compound  is 
formed  which  is  neither  acid  nor  alkaline,  and  which  may  bear  no 
more  resemblance  to  its  proximate  constituents  than  bread  bears  to 
flour  and  water,  or  rust  to  iron  and  oxygen. 

From  such  reactions  between  acids  and  sodium  hydrate,  water  is 
always  disengaged  simultaneously  with  the  saline  product,  as  may  be 
illustrated  by  the  following  examples  (compare  also  §§  61-63):  — 

NaHO     -f     HN03  =  NaNO3          -f  H2O; 

2  NaHO     -j-     H0S04  =  Na2SO4         -+-  2H2O; 

NaHO     +     C2H402  =  C2NaH3O2     +  H2O. 

Acetic  acid.  Sodium  acetate. 


§  376.]  BORAX  A   BLOWPIPE  TEST.  217 

While  recognizing  the  frequent  occurrence  of  such  reactions  as  are 
thus  represented  between  hydrated  oxides,  it  must  not  be  forgotten 
that  many  anhydrous  saline  compounds  can  be  made  by  the  direct 
combination,  under  appropriate  conditions,  of  two  oxides  which  con- 
tain no  hydrogen.  By  heating  one  jiiolecule  of  sodium  hydrate, 
or  40  parts  by  weight,  with  one  molecule,  or  23  parts  by  weight,  of 
sodium,  an  oxide  of  sodium  (Na2O)  is  obtained  which  contains  no 
hydrogen  ;  but  this  body  has  none  of  the  properties  described  by 
the  adjective  alkaline,  any  more  than  the  anhydrous  teroxide  of  sul- 
phur possesses  the  properties  suggested  to  the  mind  by  the  term 
"acid."  Now,  the  very  same  sodium  sulphate  which  results  from 
the  second  of  the  above  reactions,  may  be  prepared  by  bringing 
together  this  anhydrous  sodium  oxide  and  sulphuric  anhydride  :  — 
Na20  -f  S03  =  Na2S04. 

There  exists  another  anhydrous  oxide  of  sodium,  corresponding  in 
composition  to  the  formula  Na2O2,  and  the  same  sodium  sulphate 
can  be  made  by  heating  this  oxide  with  sulphurous  acid  gas  :  — 
Na202  +  S02  =  Na2S04. 

These  facts  show  that  a  knowledge  of  the  substances  from  which 
a  salt  may  be  made  is  not  sufficient  to  establish  any  presumption  con- 
cerning the  molecular  constitution  of  the  salt  itself. 

376.   Sodium  Biborate  or  Borax  (Na2B4O7>  10  H3O).  — Borax 

is  a  colorless,  crystalline  salt  occurring  ready  formed  in  nature. 
The  greater  part  of  that  used  in  the  arts  is  prepared  from  the 
native  boracic  acid  of  Tuscany  (§  361)  by  the  addition  of  sodium 
carbonate.  Carbonic  acid  is  set  free  and  the  borax  crystallizes 
out  from  the  solution. 

Borax  has  a  feebly  alkaline  taste  and  reaction.  When 
heated  it  bubbles  up,  loses  its  water,  and  melts  below  redness 
into  a  transparent  glass  ;  this  glass  dissolves  many  oxides  of 
the  metals,  acquiring  thereby  various  colors  characteristic  of 
these  oxides.  Hence  borax  is  much  used  as  a  blowpipe  test 
for  determining  the  presence  of  certain  oxides  of  the  met- 
als. 

Exp.  177.  —  Make  a  little  loop,  about  as  large  as  this  Q,  on  the 
end  of  a  bit  of  fine  platinum-wire  6  or  8  c.  m.  long.  Make  the  loop 
white-hot  in  the  blowpipe  flame,  and  thrust  it  while  hot  into  some 
powdered  borax  ;  a  quantity  of  borax  will  adhere  to  the  hot  wire  ; 
reheat  the  loop  in  the  oxidizing  flame  ;  the  borax  will  puff  up  at  first, 
19 


218  COMPOUNDS  OF  SODIUM.  [§  377. 

and  then  fuse  to  a  transparent  glass.     If  enough  borax  to  form  a 
solid,  transparent  bead  within  the  loop  does  not  adhere  to  the  hot  wire 
the  first  time,  the  hot  loop  may  be  dipped  a  second  time  into 
Fiif.  66.  the   powdered  borax.      When  a  transparent  glass  has  been 
O       formed  within  the  lo«p  of  the  platinum-wire,  touch  the  bead 
of  glass,  while  it  is  hot  and  soft,  to  a  speck  of  manganese  bi- 
noxide  no  bigger  than  the  period  of  this  type  ;  reheat  the 
bead  with  the  adhering  particle  of  oxide  in  the   oxidizing 
flame  ;  the  black  speck  will  gradually  dissolve,  and  on  looking 
through  the  bead  towards  the  light,  or  a  white  wall,  when  the 
oxide   has  disappeared,  the  glass  will  be  seen  to   have  as- 
sumed a  purplish-red  color. 

The  same  experiment  may  be  performed  with  iron  oxide, 
which  imparts  to  the  glass  a  yellow  color,  or  with  copper 
oxide,  which  imparts  a  bluish-green  color.  The  oxidizing 
flame  must  be  used  in  both  these  cases,  as  with  the  man- 
ganese oxide. 

The  power  which  borax  possesses  of  dissolving  metallic  oxides 
suggests  an  explanation  of  its  use  in  brazing  and  in  soldering 
the  precious  metals.  The  solder  will  only  adhere  to  a  bright 
and  clean  metallic  surface,  and  the  borax  which  melts  with  the 
solder  removes  from  the  pieces  of  metal  the  film  of  oxide  which 
would  otherwise  prevent  the  adhesion  of  the  solder.  Borax  is 
also  used  by  the  assayer  and  refiner  as  a  flux. 

377.  Other    Compounds    of    Sodium.  —  Sodium    nitrate 
(NaNO3),  a  somewhat  deliquescent  and  very  soluble  salt,  occurs 
abundantly  on  the  surface  of  the  soil  in  certain  desert  districts 
of  Peru.     It  is  employed  in  the  manufacture  of  nitric  and  sul- 
phuric acids  and  as  a  manure.     There  are  several  phosphates  of 
sodium  corresponding  to  the   different  varieties  of  phosphoric 
acid.     The  most  familiar  of  these  phosphates,  and  the  one  com- 
monly called  sodium  phosphate,  is  a  crystallized  salt  of  the  for- 
mula HNa2PO4,12  H2O- 

378.  Sodium   Sulphide.  —  Compounds   of  sodium  and  sul- 
phur may  be  formed  by  heating  sodium  sulphate  (Na2SO4)  with 
charcoal;  by  heating  sodium  carbonate  and  sulphur  together; 
and  by  boiling  sulphur  with  caustic  soda.     There  are  at  least 


§  380.]  POTASSIUM.  219 

five  different  compounds  (Na2S,  NazS2,  Na2S3,  Na2S4,  NasS6)  all 
soluble  in  water  :  when  treated  with  an  acid  they  all  give  off 
hydrogen  sulphide  (§  117)  and  from  all  except  the  first  there 
falls  a  precipitate  of  finely  divided  sulphur,  known  as  milk  of 
sulphur.  There  is  also  a  compound  (NaHS)  called  sodium  sul- 
phydrate  (hydrogen  sodium  sulphide)  analogous  in  composition 
to  sodium  hydrate  (NaHO). 

Exp.  178.  —  Into  a   small  flask  put  a   pinch  Fi»-  6?. 

of  flowers  of  sulphur  and  two  teaspoonfuls  of  a  so-  .>  | 

lution  of  caustic  soda.  Boil  the  solution  for  some 
minutes  ;  the  sulphur  disappears  and  the  liquid 
becomes  dark  colored.  To  the  solution  of  sodium 
sulphide  thus  obtained,  add  dilute  chlorhydric 
acid  until  the  mixture  turns  litmus  paper  red  ; 
observe  the  odor  of  hydrogen  sulphide  and  also 
the  precipitate  of  sulphur. 

379.  Sodium  silicates  may  be  prepared 
by  dissolving  silica  in  caustic  soda,  or  by  fusing  together  silica 
and  sodium  carbonate.  The  silicate  of  commerce  called  water- 
glass  is  of  varying  composition.  Sodium  silicate  is  an  ingre- 
dient of  common  glass,  as  has  already  been  seen.  Sodium 
hyposulphite  (Na2S2O3,  5  H2O),  is  a  crystallized  salt  much  used 
by  photographers,  because  its  aqueous  solution  is  capable  of 
dissolving  silver  chloride,  bromide  and  iodide,  —  compounds 
much  employed  by  the  photographer,  and  very  insoluble  in 
water. 


CHAPTER  XX. 
POTASSIUM  (K). 

380.  The  proximate  sources  of  sodium  compounds  are  the 
sea  and  salt  springs  and  deposits.  Potassium  compounds,  on 
the  other  hand,  are  derived  indirectly  from  the  soil.  Arable 
soils  are  produced  by  the  weathering  and  gradual  decomposition 
of  the  common  granitic  rocks.  These  rocks  contain  a  certain 
amount  of  potassium  silicate  ;  the  element  potassium  thus  be- 


220 


POT  A  SSWM-  CA  &BONA  TE. 


[§-381. 


Fig.  68. 


comes  a  normal  constituent  of  the  earthy  food  of  plants.  No 
cheap  and  easy  method  has  yet  been  devised  for  separating  the 
potassium  compounds  from  the  other  ingredients  of  the  soil. 
Plants,  however,  are  able  to  pick  out  and  assimilate  the  potas- 
sium salts  from  the  soil,  so  that  by  burning  the  plants  and 
extracting  the  ashes  with  water  a  soluble  potassium  salt  is 
obtained.  The  salt  which  is  obtained  from  the  ashes  of  plants 
by  washing  and  evaporation  is  called  potash,  or,  if  refined, 
pearlash,  and  it  is  from  this  substance  that  the  bulk  of  potas- 
sium compounds  are  obtained. 

Exp.  179.  —  Place  a  handful  of  wood-ashes  on  a  filter,  and  pour 
hot  water  over  them,  collecting  the  filtrate  in  a  bottle  and  returning 
it  upon  the  ashes  two  or  three  times,  in  order  to  obtain  a  stronger  solu- 
tion. To  exhaust  the  ashes 
of  their  potash  they  must, 
of  course,  be  treated  with 
successive  portions  of  hot 
water.  This  solution  has 
a  strong  alkaline  reaction 
upon  test-paper.  A  few 
drops  of  it,  poured  into  a 
test-tube  containing  a  little 
dilute  acid,  occasion  a  brisk 
effervescence,  a  reaction 
from  which  we  readily  sur- 
mise the  truth,  that  the 
potassium  salt  contained  in 
the  solution  is  potassium  carbonate.  By  evaporating  the  rest  of  the 
solution  to  dryness  in  a  porcelain  dish,  we  obtain  a  small  sample  of 
crude  potash. 

381.  Potassium  carbonate  (K2CO8)  is  a  hygroscopic  and  very 
soluble  salt.  When  exposed  to  damp  air  it  becomes  moist,  and 
finally  deliquesces.  In  this  respect  it  does  not  resemble  soda- 
ash,  which  is  not  hygroscopic,  and  is,  for  this  reason  among 
others,  better  adapted  than  potash  for  transportation,  storing, 
and  for  most  commercial  uses. 

Potassium  carbonate  was  the  most  important  source  of  alkali, 
until  Leblanc's  process. made  soda  cheaper  than  potash..  It  is 


§  383.]  POTASSIUM  HYDRATE.  221 

still  largely  consumed  in  the  manufacture  of  soap,  glass,  caustic 
potash  and  other  compounds  of  potassium,  but  sodium  salts 
have,  to  a  great  extent,  displaced  potassium  salts  in  commerce 
and  the  arts. 

382.  Hydrogen  Potassium  Carbonate  (HKCO3).  —  This  salt, 
which  is  commonly  called  "bicarbonate  of  potash"  (K2O,H2O, 
2  CO2),  is  prepared  by  passing  a  current  of  carbonic  acid  through 
a  strong  solution  of  potassium  carbonate  ;  crystals  of  the  bicap 
bonate   will   be    deposited,    which   are   permanent   in   the  air. 
Saleratus  is  properly  potassium  bicarbonate  ;  but  sodium  bicar- 
bonate is  often  substituted  for  it. 

383.  Potassium    Hydrate    (KHO).  —  The   manufacture   of 
potassium  hydrate  from  potassium  carbonate  resembles,  in  every 
detail,  the  preparation  of  caustic  soda  from  sodium  carbonate 
(§  373).      Potassium   hydrate    is   a   hard,    whitish    substance, 
possessing  a  peculiar  odor  and  a  very  acrid  taste.     Like  sodium 
hydrate,  it  rapidly  absorbs  moisture  and  carbonic  acid  from  the 
air,   and  since  the  potassium  carbonate  thus  formed  is  a  delir 
quescent    salt,    this    change    will  go   on  until  the  entire  mass 
of  hydrate  is  converted  into  a  sirup  of  the  carbonate  ;  whereas, 
in  the  case  of   sodium  hydrate,  the  absorption  of  water  and 
carbonic  acid  is  soon  arrested  by  the  formation   of  a  coating 
of  non-deliquescent   sodium     carbonate    upon    the   surface    of 
the    lump    of   hydrate.       Potassium    hydrate,    cast   into    small 
sticks,  is  employed  by  physicians  as  a  cautery,  —  a  use  which 
illustrates  forcibly  its  destructive  effect  upon  animal  and  vege- 
table matters.     Like  sodium  hydrate,  its  solution  destroys  ordi- 
nary  paper,   and   cannot   be   filtered   except  through  asbestos, 
or  gun-cotton.     A  clear  solution  is  best  obtained  by  decanta- 
tion  from  off  the  subsided  impurities.     In  the  chemical  labora- 
tory, solutions  of  caustic  potash  and  caustic  soda  are  in  frequent 
use  for  absorbing  acid  gases,  such  as  carbonic  acid,  and  espe- 
cially for  separating  the  hydrates  of  other  metals  from  solutions 
of  their  salts. 

Exp.  180.  —  Dissolve  a  crystal  of  blue  vitriol  (copper  sulphate) 
in  a  few  cubic  centimetres  of  cold  water,  and  add  to  the  solution 


222  POTASSIUM  OXIDIZES  READILY.  [§  334. 

several  drops  of  a  solution  of  caustic  potash.  Copper  hydrate  is 
thrown  clown  as  a  delicate,  blue,  insoluble  precipitate,  while  colorless 
potassium  sulphate  remains  in  solution. 

CuS04     -f     2KHO     =     CuH202     -f-     K2SO4. 

Copper  sulphate.  Copper  hydrate. 

384.  Potassium  (K).  —  This  element,  like  sodium,  is  made 
from  its  carbonate  by  heating  intensely  a  mixture  of  the  car- 
bonate and  charcoal,  in  accordance  with  the  reaction  :  — 

K2C03  +  2C  =  2K-f3CO. 

Potassium  is  a  silver-white  substance,  of  very  brilliant  lustre, 
which  is  brittle  at  0°,  soft  as  wax  at  ordinary  temperatures,  fuses 
at  6 2°. 5,  and  is  volatile  at  a  red-heat.  It  is  lighter  than  water, 
having  a  specific  gravity  of  only  0.865.  It  is  almost  instan- 
taneously oxidized  by  air  and  water  at  the  ordinary  temperature, 
and,  when  heated,  by  nearly  every  gas  or  liquid  which  contains 
oxygen.  Like  sodium,  it  must,  therefore,  be  collected  and  kept 
under  naphtha,  out  of  contact  with  the  air. 

Exp.  181.  —  Throw  a  piece  of  potassium,  as  large  as  a  small 
Fi  69  Pea'  uPon  some  cold  water  in  the  bottom  of  a  large  bottle, 
and  place  a  card  or  glass-plate  over  the  mouth  of  the  bot- 
tle. The  potassium  decomposes  the  water,  and  evolves 
heat  enough  to  kindle  the  hydrogen  which  is  given  off ; 
this  hydrogen  burns  with  a  purplish-red  color,  imparted  to 
the  flame  by  a  minute  quantity  of  vaporized  potassium. 
This  color  is  characteristic  of  potassium  compounds,  as  a 
yellow  color  is  characteristic  of  sodium  compounds.  The 
water  will  have  an  alkaline  reaction  from  the  formation 
of  potassium  hydrate. 

Exp.  182.  — To  a  gas-bottle  in  which  carbonic  acid  is  being 
steadily  evolved,  according  to  Exp.  75,  attach  a  chloride  of  calcium 
tube,  and  beyond  this  drying-tube  a  short  tube  of  hard  glass,  from 
which  an  exit-tube  leads  into  a  small  open  bottle,  as  shown  in 
Fig.  70.  When  the  extinction  of  a  lighted  match  in  the  open  bottle 
proves  the  apparatus  to  be  full  of  carbonic  acid,  thrust  into  the  hard 
glass-tube"  a  bit  of  potassium  as  big  as  a  pea,  previously  dried 
between  folds  of  blotting-paper,  then  gently  heat  the  potassium  with 
a  lamp.  The  potassium  will  take  fire  and  burn  at  the  expense  of  the 


§  386.]  POTASSIUM  CYANIDE.  223 

oxygen  of  the  carbonic  acid,  and  black  particles  of  carbon  will  be  de- 
posited upon  the  walls  of  the  tube.     After  the  reaction  has  ceased, 


Fig.  7O. 


and  the  tube  has  been  allowed  to  become  cold,  place  it  in  a  bottle  of 
water,  so  that  the  saline  mass  (potassium  carbonate)  may  dissolve  ; 
the  particles  of  carbon  will  then  be  seen  more  clearly,  floating  in  the 
liquid  ;  they  may  be  collected  upon  a  filter.  The  reaction  which  has 
taken  place  may  be  thus  expressed  :  — 

4  K  -f  3  C02  =  2  K2C03  +  C. 

385.  Potassium  chloride  (KCl)  is  a  subordinate  source  of 
potassium  compounds.     It  occurs   in   sea-water  and   in   brine- 
springs,  and  is  a  secondary  product  of  several  manufacturing 
operations.     Potassium  chloride  resembles  common  salt  in  ap- 
pearance and  in  taste  ;  it  is  somewhat  more  soluble  in  water 
and   volatilizes  at   a   lower  temperature.     Potassium   bromide 
(KBr)  and  iodide  (Kl)  resemble  the  chloride.     They  are  much 
used  in  medicine,  and  the  iodide  is  extensively  employed  by 
photographers. 

386.  Potassium  cyanide  (KCN)  is  a  white,  fusible,  deliques- 
cent solid  which  may  be  made  by  fusing  nitrogenous  organic 
matter   with   potassium    carbonate  or  hydrate.     It  is  of  great 
use   in   galvanic  gilding  and  silvering,   since  gold   and   silver 
cyanides  are  both  soluble  in  a  solution  of  potassium  cyanide. 
Its  solution  dissolves  silver  sulphide,  and  has,  therefore,  been 
suggested   for  household  use  in  cleaning  silver-ware  ;   photog- 
raphers sometimes  use  it  for  removing  stains  of  silver  nitrate 
from   the   hands;    but   both   these   applications   of    potassium 


224  POTASSIUM  FERRICYANIDE.  [§  387. 

cyanide  are  dangerous  and  inexpedient.  The  cyanide  is  in- 
tensely poisonous,  not  only  when  taken  internally,  but  also 
when  brought  in  contact  with  an  abrasion  of  the  skin,  a  cut 
or  scratch.  As  a  reducing  agent,  potassium  cyanide  has  great 
Fig.  71.  power ;  it  is  especially  useful  in 

blowpipe  reactions. 

Exp.  183.  —  Scoop  out  a  little  hol- 
low at  one  end  of  a  bit  of  charcoal 
8  to  12  c.  m.  long.  Introduce  into  the 
hollow  a  mixture  of  equal  parts  of  tin 
oxide  (SnO2),  dry  sodium  carbonate 
and  potassium  cyanide.  Heat  with  the 
reducing  blowpipe-flame,  for  a  minute 
or  two.  Metallic  tin  will  be  reduced 
SnO2  +  2  KCy  =  Sn  +  2  KCyO  (potassium  cyanate). 

387.  Potassium    Ferrocyanide   (K4FeCy6).  —  When  potas- 
sium carbonate  is  fused  with  nitrogenous  organic  matter  potas- 
sium  cyanide   is  formed,  as  has  been  stated  in  the  preceding 
section.     When  this  fusion  takes  place  in  the  presence  of  iron 
(as  iron  filings,  for  instance),  the  fused  mass  treated  with  water 
yields  a  solution  of  a  salt  known  as  potassium  ferrocyanide. 
This  salt  crystallizes  in  large  yellow  crystals,  and  is  met  with  in 
commerce  under  the  name  of   "yellow    prussiate   of   potash" 
nearly  in  a  state  of  purity. 

Potassium  ferrocyanide  is  a  salt  of  an  acid  called  ferro-cyan- 
hydric  acid  (H4FeCy6),  a  compound  of  hydrogen  with  the  hypo- 
thetical quadrivalent  radical  ferro-cyanogen,  FeCy6,  or  Fey. 
When  potassium  ferrocyanide  is  heated  with  sulphuric  acid,  it  is 
decomposed  in  accordance  with  the  reaction  :  — 

Potassium  ferrocyanide.  Water.  Sulphuric  acid. 

K4FeC6N6H603  +     3  H0O  +     6  H2SO4 

=  6  CO     +     2  K2S04  +     FeS04  +     3  (NH4)2SO4. 

Carbon  Potassium  Iron  Ammonium 

protoxide.  sulphate.  sulphate.  sulphate. 

This  reaction  has  already  been  taken  advantage  of  in  the  prepara- 
tion of  carbon  protoxide  (Exp.  81,  §  195). 

388.  Potassium  Ferricyanide  (K3FeCy6).  —  When  a  current 
of  chlorine  gas  is  passed  through  a  solution  of  ferrocyanide  of 


§  391.]  POTASSIUM  NITRATE.  225 

potassium  the  following  reaction  takes  place  :  —  K4FeCy6  -f-  Cl 
=  KgFeCy,.  -\-  KC1.  The  compound  K3FeCy6,  potassium  ferricy- 
anide,  may  be  obtained  in  beautiful  deep-red  crystals  by  evap- 
orating the  solution.  This  compound  is  known  in  commerce  as 
"red  prussiate  of  potash." 

Potassium  ferri cyanide  is  a  salt  of  ferri  -  cyanhydric  acid 
(HgFeCy,.),  a  compound  of  hydrogen  with  the  hypothetical  triva- 
lent  radical,  FeCy6  or  Fdcy.  The  ferro-  and  ferri-cyanides  of 
potassium  afford  valuable  means  of  identifying  iron  in  its  com- 
pounds, as  will  be  seen  in  §  477. 

389.  Potassium  sulphate  (K2SO4)  differs  from  sodium  sul- 
phate in  crystallizing  as  an  anhydrous  salt.     The  salt  enters  into 
the  composition  of  many  of   the  double  sulphates  which  are 
called  alums,  from  the  name  of  the  commonest  member  of  the 
class,  the  aluminum  and  potassium  sulphate. 

390.  Hydrogen  Potassium  Sulphate  (HKSOj.  —  This  salt, 
commonly  called  the  "  bisulphate,"  is  formed  on  a  large  scale  as 
a  residuary  product,  whenever  nitric  acid  is  manufactured  from 
potassium  nitrate.     When  ignited,  sulphuric  acid  is  given  off 
and  potassium  sulphate  remains  :  — 

2  (HKS04)  =  K3S04  -f  H2S04. 

391.  Potassium  Nitrate  (KNO3).  —  This  valuable  salt,  com- 
monly called  saltpetre,  or  nitre,  is  very  widely  diffused  in  nature. 
In  many  localities,  it  is  found  in  caverns  or  caves  in  calcareous 
formations,  but  the  chief  commercial  source  of  the  salt  is  the  soil 
of  tropical  regions,  especially  of  districts  in  Arabia,  Persia,  and 
India,  where  the  nitrate  is  found  as  an  efflorescence  upon  the  sur- 
face of  the  ground,  or  in  the  upper  portion  of  the  soil  itself.     The 
saltpetre  is  extracted  by  treating  the  earth  with  water,  and  ob- 
tained in  an  impure  state  by  evaporating   the   solution.     The 
crude  product  is  purified  by  successive  recrystallizations. 

This  natural  production  of  nitrates  appears  to  result  mainly  from 
the  putrefaction  of  vegetable  and  animal  matters,  in  presence  of  the 
air  and  of  alkaline  or  earthy  bases  capable  of  fixing  the  nitric  acid 
as  soon  as  formed.  The  well-waters  of  towns,  contaminated  by  neigh- 
boring sewers  or  cesspools,  nearly  always  contain  nitrates.  Nitrates 
are  seldom  wholly  wanting  in  a  fertile  soil,  or  in  spring  or  river  water. 


226         OXIDIZING  POWER  OF  POTASSIUM  NITRATE.     [§  392. 

The  process  of  nitrification  seems  to  be  brought  about  by  an  organized 
ferment  which  lives  in  vegetable  mould.  We  have  seen  that  the  yeast 
plant  accomplishes  the  conversion  of  sugar  into  alcohol  (§  225)  ;  some- 
thing similar  is  supposed  to  take  place  in  nitrification. 

392.  Potassium  nitrate  is  white,  inodorous  and  anhydrous, 
and  has  a  cooling,  bitter  taste.  When  pure,  it  is  permanent  in 
the  air,  —  a  fact  of  great  importance,  inasmuch  as  the  chief  use 
of  this  salt  is  in  the  manufacture  of  gunpowder.  Were  it 
hygroscopic,  like  sodium  nitrate,  it  would  not  be  applicable  to 
this  use.  It  is  very  soluble  in  water,  especially  in  hot  water ; 
it  melts  below  a  red  heat  to  a  colorless  liquid  without  loss  of 
substance,  but  at  a  red  heat  it  gives  off  oxygen,  and  suffers 
decomposition.  Its  most  marked  chemical  characteristic  is  its 
oxidizing  power. 

Exp.  184.  —  Mix  5  grms.  of  powdered  saltpetre  with  1  grm.  of 
dry,  powdered  charcoal ;  place  the  mixture  on  a  piece  of  porcelain 
Fl«.  78.  and  ignite  it  with  a  hot  wire.     When 

the  deflagration  is  over,  a  white  solid 
will  be  found  upon  the  porcelain. 
Dissolve  this  solid  in  a  few  drops  of 
water ;  the  solution  will  be  alkaline 
to  test-paper  ;  add  a  few  drops  of  a 
dilute  acid  ;  a  brisk  effervescence 
marks  the  escape  of  carbonic  acid.  The  nitrate  has  oxidized  the 
carbon  to  carbonic  acid,  part  of  which  escaped  with  the  nitrogen 
during  the  deflagration,  while  part  entered  into  combination  with  the 
potassium  :  —  4  KNO3  -f  5  C  =  2  K2CO3  -f  3  CO2  -f  4  N. 

Gunpowder  is  an  intimate  mechanical  mixture  of  soft-wood  char- 
coal, sulphur  and  potassium  nitrate,  in  the  proportions  of  70  or  80 
per  cent  of  the  nitrate  to  10  or  12  per  cent  of  each  of  the  other 
ingredients.  When  gunpowder  burns  in  a  closed  space,  the  reaction 
that  takes  place  is  quite  complex  ;  speaking  in  general  terms,  how- 
ever, we  may  say  that  the  oxygen  of  the  nitrate  combines  with  the 
carbon  to  form  carbonic  acid  and  carbonic  oxide,  while  the  sulphur  is 
retained  by  the  potassium,  and  nitrogen  is  left  free.  A  very  large  pro- 
portion of  gas,  as  compared  with  the  bulk  of  the  solid  powder,  is  thus 
evolved  when  powder  is  burned.  Moreover  gunpowder  burns  rapidly 
and  with  great  evolution  of  heat,  so  that  the  volume  of  gas,  large  at 


§  393.]  POTASSIUM  CHLORATE  AN  OXIDIZING  AGENT.      227 

any  temperature,  is  enormously  expanded  at  the  moment  of  its  forma- 
tion ;  hence  it  happens  that  the  gas  set  free  may  be  capable  of  occu- 
pying a  thousand  or  fifteen  hundred  times  as  much  space  as  the 
powder  which  generated  it.  An  enormous  pressure  is  thus  engen- 
dered at  the  spot  where  the  powder  burns,  and  to  this  pressure  some 
part  of  the  matter  which  confines  the  powder  must  yield.  In  the 
case  of  fire-arms  it  is  the  ball  which  yields  to  the  pressure  :  in  blast- 
ing it  is  the  solid  rock  itself  that  is  torn  apart. 

393.  Potassium  chlorate  (KC1O3)  is  a  white,  crystallized 
salt  much  used  in  medicine,  in  calico-printing,  in  pyrotechny, 
in  the  match-manufacture  and  in  the  chemical  laboratory,  on 
account  of  its  large  oxygen  contents.  It  is  an  oxidizing  agent 
of  the  most  vigorous  description.  At  a  red  heat  it  is  resolved 
into  potassium  chloride  and  oxygen  (Exp.  4) : — 

KC103  =  KC1  +  3  O. 

Potassium  chlorate  is  so  prompt  an  oxidizing  agent  that  mix- 
tures of  it  with  combustible  bodies  often  detonate  violently  when 
struck  or  heated.  These  combustions  are  attended  with  great 
danger  unless  very  small  quantities  be  used. 

Exp.  185.  —  Provide  a  bit  of  ordinary  phosphorus,  as  large  as  a 
pin's  head  ;  add  enough  finely  powdered  potassium  chlorate  to  cover 
the  phosphorus  ;  fold  the  mixture  tightly  in  a  small  piece  of  writing- 
paper  ;  place  the  parcel  upon  an  anvil  and  strike  it  sharply  with  a 
hammer.  The  mixture  will  explode  with  violence. 

Strong  acids  like  sulphuric,  nitric  and  chlorhydric  acids,  de- 
compose potassium  chlorate  with  evolution  of  oxides  of  chlorine, 
or  of  chlorine  and  oxygen.  The  decomposition  is  often  at- 
tended with  decrepitation,  and  sometimes  with  a  flashing  light ; 
combustibles,  like  sulphur,  phosphorus,  sugar  and  resin,  are  in- 
flamed by  the  gases  evolved. 

Exp.  186.  —  Pour  into  a  conical  test-glass  25-30  c.  c.  of  water, 
and  throw  into  the  water  some  scraps  of  phosphorus,  weighing  to- 
gether not  more  than  0.3  grm.,  and  3-4  grms.  of  crystals  of  potassium 
chlorate.  By  means  of  a  thistle-tube  bring  5  or  6  c.  c.  of  strong 
sulphuric  acid  into  immediate  contact  with  the  chlorate  at  the  bottom 
of  the  glass.  Then  withdraw  the  thistle-tube.  In  a  moment  the 


228  AMMONIUM  SALTS.  [§  394. 

phosphorus  is  kindled,  and  burns  with  vivid  flashes  of  light  beneath 
the  water.     An  evolution  of  chlorine  accompanies  the  reaction. 

Exp.  187.  —  Hub  4  or  5  gnus,  of  clean  potassium  chlorate,  free 
from  dust,  to  a  fine  powder  in  a  porcelain  mortar.  In  powdering 
potassium  chlorate,  care  must  be  taken  that  the  mortar  and  pestle  are 
perfectly  clean,  and  the  salt  is  free  from  organic  matter,  and  violent 
percussion  and  heavy  pressure  upon  the  contents  of  the  mortar  must 
be  wholly  avoided.  Place  the  powdered  chlorate  on  a  piece  of  paper, 
add  an  equal  bulk  of  dry,  powdered  sugar  to  the  pile,  and  with  the 
fingers  and  a  piece  of  card,  mix  the  two  materials  thoroughly  together. 
Mixtures  of  potassium  chlorate  and  organic  matter  are  liable  to  ex- 
plode, if  strongly  rubbed  or  but  lightly  struck.  Wrap  the  mixture 
in  a  paper  cylinder,  and  place  the  cylinder  on  a  brick  in  a  strong 
draught  of  air  ;  let  fall  upon  the  mixture  a  drop  of  sulphuric  acid 
from  the  end  of  a  glass  rod  ;  a  very  vivid  combustion  will  ensue,  with 
the  violet-colored  flame  characteristic  of  potassium. 

394.  Potassium  tartrate  (K2C4H4O6)  is  a  very  soluble  crys- 
talline salt ;  the  hydrogen  potassium  tartrate  (HKC4H4O6), 
known  in  the  crude  state  as  "  argol,"  and  when  purified  as 
"  cream  of  tartar,"  has  already  been  described  in  §  327, 


CHAPTER  XXI. 
AMMONIUM  SALTS. 

395.  By  neutralizing  an  aqueous  solution  of  ammonia  with 
nitric  acid  there  is  formed,  in  accordance  with  the  reaction 
NH3,H2O  +  HNO3  =  (NH4)NO3  -f  H2O,  a  body,  (NH4)NO3, 
corresponding  in  composition  to  potassium  nitrate  (KNO3)  ex- 
cept that  the  group  of  atoms  NH4  takes  the  place  of  the  atom 
K.  If  we  had  used  chlorhydric  acid  there  would  have  been 
formed  a  body,  NH4C1,  corresponding  to  potassium  chloride, 
KC1;  sulphuric  acid  would  give  (NH4)2SO4  corresponding  to 
K2SO4.  To  explain  the  constitution  of  these  and  similar  salts, 
the  group  of  atoms  NH4  is  regarded  as  playing  the  part  of  a 


§.397.]  AMMONIUM  SALTS.  229 

..metallic  element,  like  sodium  or  potassium,  and  has  received  the 
name  ammonium.  We  have,  however,  no  positive  evidence  of 
the  separate  existence  and  metallic  character  of  this  group  of 
atoms  NH4. 

All  ammonium  salts,  whether  solid  or  in  solution,  evolve 
ammonia-gas  (NH3)  when  heated  with  the  hydrates  of  sodium, 
potassium,  calcium  and  a  few  other  metals. 

Exp.  188. — To  a  few  cubic  centimetres  of  a  solution  of  ammo- 
nium chloride  in  a  test-tube,  add  a  few  drops  of  a  solution  of  caustic 
soda,  and  boil  the  liquid.  The  gaseous  ammonia  can  be  detected 
by  its  odor.  If  in  any  case  the  ammonia  evolved  be  in  so  small  a 
quantity  that  its  characteristic  smell  cannot  be  detected,  it  may  be 
recognized  by  its  property  of  restoring  the  blue  color  to  reddened 
litmus  paper  (§  60),  and  of  forming  white  fumes  by  contact  with  a 
rod  moistened  with  somewhat  dilute  chlorhydric  acid.  The  reaction 
may  be  formulated  as  follows .:  — 

NH4C1  4-  NaHO  ==  NaCl  -f  NH3  -f  H2O. 

396.  The  solution  of  ammonia-gas  in  water  (NH3,H2O)  may 
be  regarded  as  a  solution  of  ammonium  hydrate,  (NH4)HO, 
comparable  with  the  solution  of  caustic  soda,  NaHO,  or  caustic 
potash,  KHO.  This  solution  produces,  indeed,  many  of  the 
effects  which  the  solutions  of  the  caustic  alkalies  produce;  it 
neutralizes  acids,  and  sets  free  the  hydrates  of  many  metals  from 
solutions  of  their  salts ;  it  is  capable  of  saponifying  fats  (§  243) 
and  is,  in  short,  a  powerful  base. 

Exp.  189.  —  Dissolve  a  small  crystal  of  alum  in  6-8  c.  c.  of  water 
in  a  test-tube  and  add  ammonia-water  until  the  solution,  after  being 
well  shaken,  smells  strongly  of  ammonia.  A  gelatinous  precipitate 
of  aluminum  hydrate  will  appear  in  the  liquid. 

Ammonium  salts  are  very  numerous,  but  only  the  few  which 
are  of  present  importance  in  the  useful  arts  will  be  here  de- 
scribed. 

397.  Ammonium  Chloride  (NH4Cl).  —  This  salt,  commonly 
called  sal-ammoniac,  is  found  native  in  many  volcanic  regions. 

The  commercial  supply  of  the  salt  was  formerly  obtained  from  the 
soot  resulting  from  the  incomplete  combustion  of  camels'  dung.     The 
.20. 


230  AMMONIUM  SALTS.  [§  39$. 

raw  material,  whence  ammonium  salts  are  now  manufactured,  is 
derived  from  gas-works  and  bone-black  factories.  Coal  and  bones 
contain  a  portion  of  nitrogen  which,  during  the  process  of  distillation, 
is  partially  converted  into  ammonia  (§  68)  ;  this  ammonia  combines 
with  the  carbonic  acid  and  sulphuretted  hydrogen,  which  are  likewise 
products  of  the  distillation,  and  these  compounds  are  condensed  into 
a  somewhat  watery  liquor,  contaminated  with  tarry  and  oily  matters, 
from  which  the  ammonium  salts  are  subsequently  extracted. 

Ammonium  chloride  serves  for  the  preparation  of  ammonia 
(Exp.  27),  and  of  ammonium  carbonate.  It  is  somewhat  em- 
ployed in  dyeing,  and  also  in  certain  processes  with  metals,  such 
as  tinning,  soldering  and  silvering  copper  and  brass,  and  galvan- 
izing (zincing)  iron.  When  heated,  it  sublimes  much  below  red- 
ness, without  undergoing  fusion. 

Exp.  190.  —  Heat  a  bit  of  sal-ammoniac  on  a  piece  of  porcelain, 
and  observe  the  low  temperature  at  which  the  solid  is  completely 
converted  into  vapor. 

398.  Ammonium  sulphate  (^(NH4)2SO4)  is  a  colorless,  crystal- 
line salt  resembling  potassium  sulphate.     It  is  employed  in  the 
manufacture  of  ammonium  alum,  as  an  ingredient   of  artificial 
manures,  and  as  a  source  of  other  ammonium  salts. 

399.  Ammonium   Nitrate    ((NH4)NOS).  —  The  method   of 
preparing  this  salt,  and  its  complete  decomposition  by  heat,  have 
been  already  described  (see  Exp,  17,  §  47  and  §  67).     The  salt 
crystallizes  in  long  needles ;  it  has  a  pungent  taste,  is  very  soluble 
in  water,  and,  in  dissolving,  produces  sharp  cold. 

400.  Ammonium  Carbonates.  —  The  commercial  carbonate 
(sal-volatile)  is  a  white,  semi-transparent,  fibrous  substance,  with 
a  pungent  taste  and  a  strong  ammoniacal  smell  •  it  is  prepared, 
on  a  large  scale,  by  the  dry  distillation  of  bones,   horn  and 
other  animal  matters.     The  product  is  purified  from  empyreu- 
matic  substances  by   repeated   sublimation.      Ammonium   car- 
bonate may  also  be  obtained  by  heating  the  chloride  (or  sul- 
phate) with  calcium  carbonate  ;  the  ammonium  carbonate  sub- 
limes,   leaving   a   residue    of   calcium    chloride    (or    sulphate). 
There  are    several    ammonium    carbonates  :    the    most    perma- 
nent is  the  "  bicarbonate  "  or  hydrogen  ammonium  carbonate 


§  403.]  ISOMORPHISM.  — LITHIUM.  231 

(H(NH4)CO8).     Into  this  the   commercial   carbonate  which  is 
an  impure  product  gradually  changes. 

401.  The  sulphides  of  ammonium  correspond  to  those  of 
sodium  (§  378) ;  a  solution  of  the  sulphydrate  (NH4HS)  which 
is  colorless  when  fresh,  but  gradually  becomes  yellow  owing  to 
the  formation  of  higher  sulphides,  is  much  used  in  the  analytical 
laboratory. 

402.  Isomorphism.  —  The  resemblance  of  the  salts  of  am- 
monium to  those  of  potassium  is  rendered  more  striking  from 
the  fact,  that  in  many  cases  it  is  true  of  corresponding  salts, 
that  the  crystalline  form   of  the  two  bodies,  as  well  as  their 
texture,   color  and  lustre,   is  identical.      If  solutions  of  these 
two  salts  be  mixed,  neither  of  the  salts  can  subsequently  be 
crystallized  out  by  itself,  when  the  solution  is  evaporated ;  the 
crystals  obtained  will  be  composed  of  the  two  salts  mixed  in 
the  most  varied  proportions.      Bodies  which  are  thus  capable 
of  crystallizing  together  in  all  proportions,  without  alteration  of 
the  crystalline  form,  are  said  to  be  isomorphous  (like-formed). 


CHAPTER  XXII. 

LITHIUM,  EUBIDIUM,  CJESIUM  AND  THALLIUM. 
SPECTRUM    ANALYSIS. 

403.  Lithium  (Li).  —  This  rare  metal  occurs  as  a  constituent 
of  not  a  few  minerals,  especially  micas  and  feldspars,  but  does 
not  form  a  large  percentage  of  any  of  them.  In  very  small  pro- 
portion, it  has  been  recognized  in  sea-water,  mineral-waters  and 
almost  all  spring-waters,  in  milk,  tobacco  and  human  blood.  It 
is  a  widely-diffused,  but  not  abundant  substance. 

Metallic  lithium  resembles  sodium  and  potassium.  It  is  the 
lightest  of  all  known  solids  which  include  no  air,  its  specific 
gravity  being  only  0.59.  The  atomic  weight  of  the  element 


232  SPECTRVM  ANALYSIS.  [§  494. 

is  also  low ;  namely,  7.  In  its  chemical  relations,  lithium 
closely  resembles  sodium  and  potassium,  but  is  somewhat  less 
energetic. 

All  the  volatile  lithium  compounds  color  a  gas-,  alcohol-  or 
blowpipe-flame  carmine-red.  The  most  delicate  reaction  for  the 
detection  of  lithium,  the  test  which  has  revealed  its  existence 
in  a  great  variety  of  substances  which  were  never  imagined  to 
contain  it,  is  the  presence  of  one  bright  line,  of  a  peculiar  red, 
in  the  spectrum,  seen  on  looking  through  a  glass  prism  at  a 
flame  colored  with  a  lithium  compound. 

404.  Spectrum  Analysis.  —  "We  have  had  occasion  to  ob- 
serve that  certain  chemical  substances,  like  boracic  acid  and  salts 
of  sodium,  potassium  and  lithium,  impart  peculiar  colors  to  the 
blowpipe  flame,  or  to  any  other  hot  and  colorless  flame.  If 
these  colored  flames  are  looked  at  through  a  prism,  a  narrow 
pencil  of  the  colored  light  being  directed  through  a  slit  upon 
the  prism,  it  will  be  seen  that  each  different  flame  produces  a 
peculiar  spectrum,  consisting  of  one  or  more  distinct  bright 
lines  of  colored  light  and  bearing-  no  resemblance-  to  the  continu- 
ous band  of  rainbow-colors  which  constitutes  the  common  spec- 
trum produced  by  a  pencil  from  any  source  of  white  light. 
Thus,  the  spectrum  of  the  yellow  sodium  flame  consists  of  a 
single,  bright,  yellow  line  ;  the  purple  potassium  flame  gives 
a  spectrum  containing  two  bright  lines,  one  lying  at  the  ex- 
treme red  and  the  other  at  the  extreme  violet  end,  and  another, 
fainter  red  line ;  while  the  lithium  spectrum  consists  of  a  very 
characteristic  red  line  and  a  fainter  orange  line. 

The  peculiar  lines  which  characterize  the  spectrum  of  any 
element  are  invariably  produced  by  that  element,  and  never 
by  any  other  substance,  and  not  only  the  color  and  number 
of  lines,  but  their  position  in  the  normal  spectrum,  always  re- 
main unaltered.  When  the  spectrum  of  a  flame  colored  with 
a  mixture  of  sodium  and  potassium  salts  is  examined,  the  yel- 
low line  of  sodium  is  seen  in  its  place,  and  the  red  and  purple 
lines  of  potassium  are  as  visible  in  their  respective  positions  as 
if  no  sodium  had  been  present.  This  example  illustrates 


§  405.]  DELICACY  Off  SPECTRUM  ANALYSIS.  233 

one  great  advantage  which  the  use  of  the  prism  gives,  — - 
the  unaided  eye  cannot  distinguish  the  potassium  color  in  the 
presence  of  the  intense  sodium-yellow,  the  brighter  color  hiding 
the  paler  •  but  with  the  prism  it  is  easy  to  detect  each  of  several 
ingredients  of  a  mixture  by  the  appearance  of  its  characteristic 
lines. 

A  new  method  of  analysis,  of  extreme  delicacy,  is  based 
upon  these  facts.  Spectrum  analysis  is  competent  to  detect 
the  *,rorW.innF  of  a  gramme  of  sodium,  or  the  ^^^  of 
a  gramme  of  lithium,  and  many  other  elements  in  incredibly 
small  proportions.  So  extreme  is  the  delicacy  of  the  method, 
that  it  brings  into  plain  sight  minute  quantities  which  alto- 
gether escape  the  coarser  process  of  analysis,  and  reveals,  as 
substances  common  in  familiar  things,  elements  which  were 
long  supposed  to  be  of  extreme  rarity.  Thus,  the  presence  of 
lithium,  formerly  considered  a  rare  element  peculiar  to  a  few 
obscure  minerals,  has  been  demonstrated  by  spectrum  analysis 
in  many  drinking-waters,  in  tea,  tobacco,  milk  and  blood.  A 
still  more  striking  illustration  of  the  value  of  spectrum  analysis 
is  to  be  found  in  the  discovery  of  a  number  of  new  elementary 
bodies  by  its  means ;  among  these  elements  are  rubidium, 
caesium,  thallium,  indium,  and  gallium. 

The  methods  and  processes  of  spectrum  analysis  are  not  appli- 
cable to  colored  artificial  lights  alone  ;  they  have  been  applied 
with  encouraging  success  to  the  lights  of  various  quality  which 
emanate  from  the  sun,  the  stars  and  the  nebulae ;  but  the 
details  of  these  observations  belong  rather  to  physics  than  to 
chemistry. 

405.  Rubidium  and  Caesium  (Rb  and  Cs).  —  These  two 
elements  are  always  found  together,  and  in  association  with 
potassium.  Though  extensively  diffused,  they  generally  occur 
in  very  minute  quantities.  Rubidium  seems  to  be  rather  the 
more  abundant.  Ten  kilogrammes  of  the  mineral  water  in 
which  these  metals  were  first  discovered  yield  not  quite  two 
milligrammes  of  csesium  chloride,  and  about  two  and  a  half 
milligrammes  of  rubidium  chloride.  The  properties  of  both 
20* 


234  THALLIUM.  — SILVER.  [§406. 

rubidium  and  caesium  differ  from  those  of  sodium  and  potassium, 
not  in  kind  but  only  in  degree.  They  are  therefore  classed  with 
sodium  and  potassium  as  alkali-metals.  The  atomic  weight  of 
rubidium  is  85.7,  of  caesium  133. 

406.  Thallium  (Tl).  —  Thallium  is  a  malleable,  ductile  metal 
resembling  lead  in  external  characters.  It  is  found  in  certain 
varieties  of  iron  pyrites.  The  properties  of  thallium  are  inter- 
mediate between  those  of  lead  and  those  of  sodium  and  potas- 
sium. Like  the  alkali-metals,  it  replaces  hydrogen  atom  for 
atom;  its  atomic  weight  is  204. 


CHAPTEE  XXIII. 
SILVER  (Ag)  — THE  ALKALI-METALS. 

407.  Silver  is  a  widely-diffused  and  quite  abundant  element, 
but  in  its  mode  of  occurrence  it  differs  widely  from  the  alkali- 
metals  which  we  have  just  been  studying.  In  the  first  place,  it 
frequently  occurs  native,  both  pure,  and  alloyed  with  mercury, 
copper  and  gold, —  a  mode  of  occurrence  quite  impossible  for 
the  alkali-metals,  because  of  their  readiness  to  combine  with  the 
elements  of  air  and  water.  The  metal  more  commonly  occurs  in 
combination  with  sulphur,  mixed  with  sulphides  of  lead,  anti- 
mony, copper  and  iron.  It  is  from  argentiferous  sulphides  that 
the  larger  part  of  the  silver  of  commerce  is  extracted,  and, 
among  ores  of  this  kind,  the  argentiferous  lead  sulphide  (galena) 
is  the  most  abundant.  Combinations  of  silver  with  selenium, 
tellurium,  chlorine,  bromine  and  iodine  are  also  to  be  enumerated 
among  silver-containing  minerals  ;  of  these  the  chloride  (horn- 
silver)  occurs  in  quantities  large  enough  to  make  it  valuable  as 
an  ore  of  the  metal.  It  is  noticeable,  that  the  only  elements 
which  are  extracted  in  any  quantity  from  their  chlorides  as  ores, 
are  sodium,  potassium  and  silver.  A  small  proportion  of  silver 


§408.]  SILVER.  — THE  TERM  METAL.  235 

exists  in  sea-water  (about  1  milligramme  in  100  litres),  and 
its  presence  has  been  recognized  in  common  salt,  in  chemical 
products  in  the  making  of  which  salt  is  used,  in  various  sea- 
weeds, in  the  ashes  of  land-plants,  in  the  ash  of  ox-blood,  and 
probably  also  in  coal.  In  sea-water  it  exists,  as  sodium  and 
potassium  do,  in  the  form  of  chloride. 

408.  Silver  (Ag).  —  The  element  silver  is  much  more  famil- 
iarly known  than  any  of  its  compounds  :  known  from  the 
earliest  ages,  this  metal  has  always  been  prized  as  much  for  its 
beauty  as  for  its  rarity.  White,  brilliantly  lustrous,  susceptible 
of  an  admirable  polish,  wonderfully  malleable  and  ductile,  the 
best  known  conductor  of  heat  and  electricity,  fusible  only  at 
a  very  elevated  temperature,  and  permanent  in  the  air,  whether 
hot  or  cold,  wet  or  dry,  it  represents  and  embodies  in  the  com- 
pletest  sense  all  that  is  commonly  understood  by  the  term 
metal. 

This  word  metal  cannot  be  strictly  denned ;  it  is  a  conven- 
tional term,  vaguely  used  because  expressing  a  vague  idea.  Thus 
metals  would  all  be  solid  were  not  mercury,  and  perhaps  caesium, 
fluid ;  they  are  generally  heavy,  but  lithium,  sodium  and  potas- 
sium float  upon  water  :  they  have  all  a  peculiar  lustre,  called 
metallic  ;  but  this  lustre  does  not  characterize  metals  alone,  for 
coke  and  graphite,  galena,  molybdenite,  and  many  other  minerals 
often  exhibit  a  similar  lustre ;  they  may  all  be  said  to  be  opaque, 
but  gold  may  be  beaten  out  so  thin  as  to  transmit  a  greenish 
light.  While  it  is  not  possible  to  define  the  term  metal  with 
precision  from  chemical,  any  more  than  from  physical  proper- 
ties, one  general  chemical  fact  deserves  attention  in  this  connec- 
tion ;  —  the  so-called  non-metallic  elements  unite  with  oxygen 
and  hydrogen  to  form  acids ;  while  the  metallic  elements  unite 
with  oxygen  and  hydrogen  to  form  bases,  This  general  fact, 
however,  does  not  give  a  sharp  line  of  demarcation,  as  some 
elements  form  both  acids  and  bases ;  thus  in  the  case  of 
arsenic,  while  there  is  an  arsenic  terchloride,  there  are  also 
arsenites  and  arseniates  of  various  metals.  In  the  table 
on  page  256  the  elements  preceding  gold  are  those  usually 


236  PROPERTIES  OF  SILVER.  [§  409. 

known  as  non-metallic  :  those  which  follow  are  the  metallic  ele- 
ments. 

409.  Silver    combines   slowly   with   chlorine,   bromine   and 
iodine,  and  promptly  with  sulphur.     The  tarnishing  of  silver  is 
due  to  the  formation  of  a  thin  film  of  the  black  sulphide  over 
the  metallic  surface,  by  combination  between  the  silver  and  tho 
sulphur  of  the  sulphuretted  hydrogen  which  is  often  present  in 
the  air  of  towns  and  houses.     The  specific  gravity  of  silver  in 
10.5,  and  its  atomic  weight  108. 

410.  The  physical  and  chemical  qualities  of  silver  fit  it  to 
serve  as  a  medium  of  exchange,  and  as  the  material  of  jewelry 
and  plate.     But  as  the  pure  metal  would  be  rather  too  soft 
for  ordinary  use,  it  is  hardened  by  combining  with  it  a  small 
proportion  of  copper.     The  proportion  of  copper  in  the  "  stand- 
ard "  silver  employed  for  coinage  varies  in  different  countries  : 
—  in  the  United  States  and  in  France  it  is  10  per  cent ;  in 
Great  Britain  it  is  7.5  per  cent ;    in  Germany  it   is   25  per 
cent. 

Exp.  191.  —  Place  one  or  two  dimes  in  a  small  flask,  and  cover 
them  with  nitric  acid  diluted  with  two  parts  of  water.  Warm  the 
flask  gently  in  a  place  where  there  is  a  good  draught  of  air  ;  the  coins 
will  gradually  dissolve,  with  evolution  of  a  gas,  nitric  oxide,  which, 
on  contact  with  air,  produces  the  abundant  red  fumes  which  escape 
from  the  flask  ;  add  more  nitric  acid,  from  time  to  time,  if  necessary 
to  complete  the  solution.  The  blue  solution  contains  both  the  silver 
and  the  copper  dissolved  in  nitric  acid. 

Place  in  the  blue  solution  two  or  three  copper  coins,  and  leave  the 
flask  at  rest  for  some  days  in  a  warm  place.  Then  collect  the  little 
plates  of  pure  silver,  which  have  separated  from  the  solution,  upon  a 
filter,  and  wash  them,  first  with  water,  and  then  with  ammonia- water, 
until  the  ammonia-water  no  longer  shows  any  tinge  of  blue.  This 
silver,  washed  finally  with  water  and  dried,  is  wellnigh  pure  ;  if  it  be 
again  dissolved  in  nitric  acid,  the  solution  will  contain  nearly  pure 
silver  nitrate. 

411.  Silver  Nitrate  (AgNO3). — This  salt,  as  we  have  al- 
ready seen,  is  obtained  in  solution  by  dissolving  silver  in  nitric 
acid.     When  such  a  solution  is  evaporated  to  the  point  of  crys- 


§  412.]  SALTS  OF  SILVER.  237 

tallizatioii,  the  nitrate  is  obtained  in  transparent,  anhydrous, 
tabular  crystals,  which  are  soluble  in  their  own  weight  of 
cold  water,  and  in  half  their  weight  of  hot  water.  The  fused 
salt  is  used  in  surgery  as  a  caustic,  under  the  name  of  lunar 
caustic. 

Silver  nitrate,  when  pure,  is  not  altered  by  exposure  to  sun- 
light ;  but  if  it  be  in  contact  with  organic  matter,  light  readily 
decomposes  it,  and  a  black,  insoluble  product  is  formed  of  no 
ordinary  stability.  Hence  the  solution  of  the  nitrate  stains  the 
skin  black,  and  the  salt  forms  the  basis  of  an  indelible  ink 
used  for  marking  linen  and  other  fabrics.  Silver  nitrate  is  much 
used  in  photography. 

412.  Silver  chloride  (AgCl)  occurs  native  sometimes  in  cubi- 
cal crystals  and  sometimes  in  compact,  semi-transparent  masses, 
which,  from  their  general  appearance,  have  given  the  mineral  the 
name  of  horn-silver.  Silver  chloride  may  be  precipitated  from 
any  soluble  silver  salt  by  adding  to  the  silver  solution  chlorhy- 
dric  acid,  or  the  solution  of  any  soluble  chloride.  Silver  chlo- 
ride is  insoluble  in  water  and  acids,  but  is  dissolved  by  am- 
monia-water. Exposed  to  the  light,  it  is  partly  decomposed 
and  becomes  dark  colored.  Silver  iodide  and  bromide  are  pre- 
pared by  adding  a  solution  of  a  soluble  iodide  or  bromide,  to  a 
solution  of  some  silver  salt. 

Exp.  192.  —  Fill  three  test-tubes  one-third  full  of  water,  and  pour 
into  each  a  few  drops  of  a  moderately  strong  solution  of  silver  ni- 
trate. Add  to  the  first  test-tube  2  or  3  c.  c.  of  a  solution  of  sodium 
chloride,  and  shake  the  tube  violently  ;  a  dense,  white,  curdy  precipi- 
tate of  the  silver  chloride  will  be  produced.  Add  to  the  second  test- 
tube  2  or  3  c.  c.  of  a  solution  of  potassium  bromide,  and  shake  the 
tube  ;  a  yellowish  precipitate  of  silver  bromide  will  be  thrown  down. 
Add  to  the  third  test-tube  1  or  2  c.  c.  of  a  solution  of  potassium  iodide, 
and  shake  up  the  liquid  ;  a  pale-yellow  flocculent  deposit  of  silver 
iodide  will  be  formed. 

Withdraw  from  each  test-tube  a  portion  of  the  precipitate  it  con- 
tains, and  try  to  dissolve  each  precipitate  in  moderately  strong  nitric 
acid  ;  the  attempt  will  fail,  for  these  silver  salts  are  insoluble  in  nitric 
acid. 

Withdraw  from  each  test-tube  another  portion  of  the  precipitate  it 


238  PHOTOGRAPHY.  [§  41$. 

contains,  and  treat  each  precipitate  with  ammonia- water ;  the  silver 
chloride  will  dissolve  easily,  the  bromide  less  easily,  the  iodide  with 
difficulty.  Lastly,  pour  upon  the  remnants  of  the  original  precipi- 
tates in  the  three  test-tubes  a  moderately  strong  solution  of  sodium 
hyposulphite  ;  all  three  precipitates  will  immediately  dissolve. 

Exp.  193.  —  Precipitate  some  curdy  silver  chloride  by  adding 
sodium  chloride  solution,  or  chlorhydric  acid,  to  a  solution  of  silver 
nitrate,  so  long  as  any  precipitate  is  produced.  Throw  the  precipi- 
tate upon  a  filter,  and  wash  it  with  water  ;  then  open  the  filter,  spread 
the  chloride  evenly  over  it,  and  place  it  in  direct  sunlight.  The  white 
precipitate  rapidly  changes  to  violet  on  exposure  to  the  sun's  rays, 
the  depth  of  shade  increasing  as  the  action  of  the  light  continues. 
Upon  the  facts  illustrated  in  this  and  the  preceding  experiments  the 
main  processes  of  photography  depend. 

413.  Other  Silver  Compounds.  —  Silver  oxide  (Ag2o)  cor- 
responds to  sodium  oxide  (Na2O).     It  is  decomposed  below  a 
red  heat,   giving  up  its  oxygen.     The  hydrate  AgHO  is  very 
slightly  soluble  in  water  giving  an  alkaline  reaction.     At  60°  it 
is  converted  into  the  oxide  (Ag2O). 

Silver  cyanide  (AgCN)  is  a  white  powder  insoluble  in  water. 
It  is  soluble  in  potassium  cyanide,  and  so  dissolved  is  used  in 
electro-plating.  Silver  sulphide  (Ag2S)  occurs  as  a  native  min- 
eral. Silver  sulphate  (Ag2SO4)  is  formed  when  metallic  silver 
is  boiled  with  strong  sulphuric  acid.  The  reaction  which  takes 
place  is  :  — 

2  Ag  +  2  H2S04  =  Ag2S04  +  2  H2O  +  SOa. 

414.  Photography.  —  The  chemical  changes  which  the  salts  of 
silver  undergo,  when  exposed  to  light,  are  the  basis  of  the  art  of  pho- 
tography, not  because  these  are  the  only  salts  which  are  affected  by 
light,  but  because  none  are  so  advantageous,  on  the  whole. 

In  order  to  get  a  photograph  upon  glass,  a  transparent  film  capable 
of  holding  the  necessary  silver  salt  must  first  be  attached  to  the  glass 
plate.  Collodion,  a  solution  of  a  variety  of  gun-cotton  in  a  mixture 
of  alcohol  and  ether,  is  the  material  of  this  film.  To  the  collodion  is 
added  a  solution  of  potassium,  cadmium  or  ammonium  iodide,  or  a 
mixture  of  these  salts. 

The  collodion  thus  prepared  is  poured  rapidly  over  a  clean  and  dry 
surface  of  plate-glass  ;  the  volatile  solvents  evaporate  rapidl}",  and  as 


§  414.1  PHOTOGRAPHY.  239 

soon  as  the  film  is  coherent,  the  glass  is  allowed  to  remain  tor  several 
minutes  in  a  bath  of  silver  nitrate,  very  slightly  acidified  with  acetic 
or  dilute  nitric  acid.  A  yellow  layer  of  silver  iodide  is  produced  in 
the  film,  and  potassium,  cadmium  or  ammonium  nitrate  dissolves  in 
the  bath.  The  plate  is  then  exposed  in  the  camera  for  a  few  seconds. 
When  removed,  no  image  is  perceptible  ;  but  on  pouring  over  the  film 
a  solution  of  gallic  or  pyrogallic  acid  in  alcohol  and  acetic  acid,  or  a 
solution  of  ferrous  sulphate  mixed  with  a  few  drops  of  a  weak  solu- 
tion of  silver  nitrate,  the  image  will  be  developed,  slowly  or  rapidly, 
according  to  the  nature  and  strength  of  the  developing  liquid,  the 
degree  of  exposure,  and  the  intensity  of  the  light.  The  illuminated 
portions  of  the  picture  will  appear,  under  the  action  of  the  developer, 
more  or  less  black,  while  the  shaded  portions  will  retain  the  yellow 
color  of  the  iodide.  As  soon  as  the  details  of  the  shaded  portions 
appear,  the  liquid  is  washed  off  and  the  development  arrested.  A 
saturated  solution  of  sodium  hyposulphite  is  then  poured  over  the  film 
to  dissolve  off  the  yellow  silver  iodide  where  it  has  not  been  affected 
by  the  light ;  only  the  reduced  portions  of  silver  remain,  and  they  ap- 
pear more  or  less  opaque.  The  plate  must  finally  be  very  thoroughly 
washed  to  remove  all  traces  of  the  hyposulphite,  and  then  dried  and 
varnished  on  the  collodion  side  to  protect  the  film  from  injury. 

From  the  glass  "  negative  "  thus  produced,  "  positive  "  pictures  on 
paper  may  be  printed.  The  paper  is  floated  for  five  minutes  on  a 
solution  of  sodium  or  ammonium  chloride  ;  when  dried,  it  is  floated 
in  a  dark  room,  for  five  minutes,  on  its  salted  surface,  in  a  solution  of 
silver  nitrate,  and  again  dried.  To  produce  the  positive  picture,  the 
paper  is  exposed  to  light  under  the  negative  to  be  copied,  until  the 
lights  of  the  picture  are  of  a  pale  lilac  hue,  and  the  shades  of  a  deep 
bronze  color.  After  being  thoroughly  washed,  the  paper  is  trans- 
ferred to  a  "  toning  "  bath,  which  consists  of  a  very  dilute  solution  of 
hydrogen  sodium  carbonate  ("  bicarbonate  of  soda  ")  with  a  minute 
proportion  of  gold  chloride.  The  picture  is  kept  in  motion  while  in 
this  bath  ;  it  remains  there  until  its  shades  have  acquired  a  deep  pur- 
ple-black color.  It  is  only  in  those  parts  of  the*picture  in  which  the 
silver  has  been  well  reduced  that  this  toning  effect  is  produced.  The 
picture  is  again  washed  in  water,  and  soaked  for  fifteen  minutes  in  a 
solution  of  sodium  hyposulphite,  in  order  to  remove  all  the  silver 
chloride  which  is  contained  in  the  substance  of  the  paper.  Finally, 
the  picture  must  be  soaked  for  twenty-four  hours  in  water  which  is 
constantly  renewed,  in  order  to  wash  away  every  trace  of  the  com- 


240  THE  ALKALI   GROUP.  [§  41 5. 

pound  sodium  and  silver  hyposulphite.  No  photograph  will  keep 
long,  unless  the  silver  chloride  has  been  completely  dissolved  by  the 
hyposulphite,  and  the  compound  hyposulphite  washed  away  with  a 
thoroughness  that  leaves  no  trace  behind.  If  the  first  condition  is 
not  fulfilled,  diffused  daylight  will  alter  the  picture  ;  if  the  second 
condition  is  not  complied  with,  yellow  or  brown  stains  will  ultimately 
destroy  the  picture. 

As  in  every  other  art  which  embraces  many  details,  and  demands 
a  trained  eye  and  hand,  eminent  skill  in  photography  can,  as  a  rule, 
be  acquired  only  by  long  practice. 

415.  The  Alkali  Group,  —  The  metals  which  must  plainly 
be  classed  together  under  this  head  are  sodium,  potassium,  (am- 
monium), lithium,  rubidium  and  caesium.  Two  other  metals  are 
better  classed  with  this  group  than  elsewhere,  but  their  likeness 
to  the  alkali-metals  is  but  partial,  and  in  many  respects  their 
properties  are  quite  unlike  those  of  the  six  metals  just  enumer- 
ated ;  these  two  metals  are  silver  and  thallium.  The  common 
properties  of  the  alkali-metals  are  mainly  these ;  —  they  have 
the  lustre  of  silver,  are  soft,  easily  fusible,  and  volatile  at  high 
temperatures ;  they  unite  greedily  with  oxygen,  and  decom- 
pose water  with  facility,  forming  basic  hydrates  which  are  very 
caustic  and  intensely  alkaline  bodies,  not  to  be  decomposed  by . 
heat ;  their  carbonates,  sulphates,  sulphides  and  chlorides,  and 
indeed  the  vast  majority  of  their  salts,  are  soluble  in  water,  and 
each  metal  forms  but  one  chloride,  one  bromide  and  one  iodide  ; 
they  all  form  basic  hydrates,  and  never  an  acid  hydrate ;  they 
occur  in  nature  in  modes  analogous,  though  not  the  same ;  their 
corresponding  salts  are  often,  though  not  always,  isomorphous  ; 
lastly,  there  is  a  general,  though  not  absolute,  uniformity  among 
the  formulas  of  the  compounds  into  which  these  elements  enter ; 
so  that,  if  a  compound  of  a  given  composition  is  proved  to 
exist  for  one  of  these  elements,  the  strong  presumption  is  that 
analogous  compounds  with  all  the  other  elements  of  the  group 
exist  likewise  with  properties  similar,  though  not  identical. 

Silver  and  thallium  present,  on  the  whole,  so  few  points  of 
resemblance  to  the  alkali  metals  that  they  would  not  be  com- 
prehended in  the  same  group  with  them  were  it  not  for  one 


§417.]     THE  ALKALI  METALS  UN1VALENT.— CALCIUM.     241 

consideration  weighty  enough  to  turn  the  balance  when  the 
discussion  of  other  properties  leaves  the  matter  in  doubt.  So- 
dium, potassium  (ammonium),  lithium,  caesium,  rubidium,  sil- 
ver and  thallium  all  replace  hydrogen,  atom  for  atom.  All 
these  elements  are  exchangeable  for  hydrogen  and  with  each 
other,  atom  for  atom,  and  in  the  present  state  of  the  science 
they  must  be  regarded  as  the  only  metals  thus  equivalent  to 
hydrogen.  The  atoms  of  the  elements  of  the  chlorine  group, 
including  fluorine  in  that  designation,  and  of  the  seven  ele- 
ments above  enumerated,  are  exchangeable  for  the  same  num- 
ber of  atoms  of  hydrogen ;  each  atom  is  worth  one  in  ex- 
change, and  these  elements  are  therefore  said  to  be  univalent 
(see  §  74). 


CHAPTEE  XXIV. 
CALCIUM,  STRONTIUM,  BARIUM  AND  LEAD. 

CALCIUM  (ca). 

416.  The  metal  calcium  is  a  constituent  of  several  of  the 
commonest  and  most  important  minerals ;  it  forms  a  very  con- 
siderable portion  —  perhaps  as  much  as  one-sixteenth  —  of  the 
solid  crust  of  the  earth.     The  metal  itself  is  yellowish-white, 
lustrous  and  ductile,  and  suffers  no  change  in  dry  air  at  the 
ordinary  temperature.     In  moist  air  it  oxidizes  quickly,  and  it 
decomposes  water  with  evolution  of  hydrogen.     At  a  red  heat 
it  melts,  and,  if  oxygen  be  present,  takes  fire  and  burns  with 
a  bright  light.     It  is  a  bivalent  element;   its  atomic  weight 
is  40. 

417.  Calcium  carbonate  (CaCO3)  occurs  in  nature  in  many 
different  forms,  sometimes  finely  crystallized,  sometimes  in  an 
amorphous  condition.     Limestone,  chalk,  marble,  calc-spar  and 
coral  are  calcium  carbonate  ;  the  shells  of  shell-fish  are  almost 

21 


242  SOLUBILITY  OF  CALCIUM  CARBONATE.         [§  418. 

entirely  composed  of  it,  and  it  is  an  important  constituent  of 
dolomite,  marl  and  many  other  rocks  and  minerals. 

In  all  its  varieties  calcium  carbonate  is  readily  attacked  by 
acids,  even  if  these  be  dilute  ;  the  action  is  attended  with  effer- 
vescence, owing  to  the  expulsion  of  carbonic  acid  and  the  escape 
of  this  gas  through  the  liquid  :  — 

CaC03  +  2  HC1  =  CaCl2  +  CO2  -f  H2O. 

418.  Calcium  carbonate,  though  tasteless,  is  slightly  soluble 
in  water,  and  the  solution  exhibits  a  faint  alkaline  reaction ;  it 
is,  however,  rather  freely  soluble  in  water  charged  with  carbonic 
acid  (§  192). 

Exp.  194.  —  Place  in  a  test-tube  20  or  30  drops  of  lime-water, 
and  as  much  pure  water  ;  in  the  mixture,  immerse  the  delivery-tube 
of  a  bottle  from  which  carbonic  acid  gas  is  being  evolved  (Exp.  75). 
Calcium  carbonate  will  be  thrown  down  at  first,  but  after  a  while,  as 
the  water  in  the  test-tube  becomes  saturated  with  carbonic  acid,  the 
precipitated  carbonate  will  re- dissolve,  and  there  will  be  obtained  a 
perfectly  clear  solution,  which,  in  spite  of  the  large  proportion  of 
carbonic  acid  contained  in  it,  has  a  decided  alkaline  reaction.  By 
boiling  the  solution,  so  that  a  portion  of  its  carbonic  acid  may  be  ex- 
pelled, the  calcium  carbonate  can  be  again  precipitated.  So,  too,  if 
the  liquid  be  left  exposed  to  the  air,  it  will  gradually  give  off  car- 
bonic acid,  and  become  turbid  from  deposition  of  calcium  carbonate. 

To  the  solubility  of  calcium  carbonate  in  water  containing  carbonic 
acid,  and  to  the  fact  that  on  the  escape  of  the  carbonic  acid  the  cal- 
cium carbonate  is  deposited,  is  clue  the  formation  of  calcareous  petri- 
factions, of  stalactites  and  stalagmites,  of  the  stones  called  tufa  and 
travertine,  and  of  many  deposits  of  crystallized  calcium  carbonate. 
Whenever  water,  charged  with  calcium  carbonate,  flows  out  from  the 
earth  into  the  open  air,  or  trickles  into  hollows  or  caverns  within  the 
earth,  carbonic  acid  is  given  off  in  the  gaseous  state,  and  calcium  car- 
bonate is  deposited.  Stalactites  are  the  pendent  masses,  like  icicles, 
which  hang  from  the  roofs  of  caverns,  and  the  walls  of  cellars, 
bridges  and  like  covered  ways  ;  stalagmites  are  the  opposite  masses 
which  grow  up  out  of  the  drops  of  water  which  fall  from  the  stalac- 
tites above  them,  before  all  the  carbonate  has  been  deposited. 

419.  Calcium    Oxide    (CaO). — On   being   heated,    calcium 
carbonate  begins  to  give  off  carbonic  acid  at  a  low  red  heat. 


§  421.]         CALCIUM  HYDRATE  OR  SLAKED  LIME.  243 

and  at  full  redness  is  completely  resolved  into  calcium  oxide, 
commonly  called  quick-lime,  and  carbonic  acid.  For  use  in 
the  arts,  limestone  is  burned  in  special  furnaces,  of  peculiar 
construction,  called  lime-kilns,  some  of  which  are  so  arranged 
that  they  may  be  kept  in  operation  for  years  without  inter- 
mission. 

Calcium  oxide  is  infusible  at  the  most  intense  heat  at  our 
present  command,  and  is,  therefore,  used  for  making  crucibles  in 
which  the  most  refractory  metals  are  melted  by  the  aid  of  the 
compound  blowpipe. 

420.  Calcium  Hydrate  (CaH2O2).  —  When  water  is  brought 
in  contact  with  calcium  oxide,  the  latter  swells  up  and  falls  to 
powder ;  a  large  amount  of  heat  is  evolved,  and  there  is  ob- 
tained a  compound  of  calcium,  hydrogen  and  oxygen,  commonly 
called  slaked  lime,  or  in  chemical  language  calcium  hydrate :  — 
CaO  +  H20  =  CaH202. 

Exp.  195. —  Place  a  lump  of  recently-burned  quick-lime,  weigh- 
ing about  30  grms.,  upon  a  large  earthen  plate  ;  pour  upon  the  lime 
some  15  or  20  c.  c.  of  water,  and  observe  how  much  the  lime  increases 
in  bulk  as  it  is  converted  into  calcium  hydrate.  The  heat  of  the  mass 
may  be  shown  by  thrusting  an  ordinary  friction-match  into  the  middle 
of  it  ;  inflammation  will  ensue. 

So  much  heat  is  developed  during  the  union  of  water  with  lime, 
that  wood  will  quickly  be  brought  to  the  kindling  temperature  and 
inflamed,  if  it  happen  to  be  in  contact  with  large  masses  of  these 
substances  reacting  upon  one  another.  Fires  are  very  frequently 
occasioned  by  the  access  of  water  to  ships  or  warehouses  in  which 
quick-lime  is  stored. 

421.  When  lumps  of  quick-lime  are  exposed  to  the  air  they 
slowly  absorb  both  water  and  carbonic  acid,  and  after  a  while 
fall  to  powder.     This  powder  is   known  as   air-slaked   lime. 
When  hydrate  of  calcium  is  stirred  into  water,  there  is  formed 
not  only  a  true  solution,  lime-water,  which  may  be  obtained 
clear  and  colorless  by  filtration,  but  also  a  turbid  liquor  consist- 
ing of  particles  of  solid  hydrate  of  calcium  diffused  through  the 
lime-water ;  this  liquor  is  known  as  milk  or  cream  of  lime, 
according  to  its  consistency. 


244  CALCIUM  HYDRATE. —MORTAR.  '[§422. 

Both  milk  of  lime  and  dry  calcium  hydrate  absorb  readily 
carbonic  acid  and  hydrogen  sulphide.  For  this  purpose  they  are 
used  in  the  purification  of  coal-gas.  On  this  property  of  absorb- 
ing carbonic  acid  depends  also  in  great  measure  the  use  of  lime 
in  mortar. 

Mortar  is  commonly  prepared  by  mixing  1  part  of  quick-lime  with 
water  enough  to  form  a  thin  paste,  then  adding  3  or  4  parts  of  coarse, 
sharp  sand,  and  thoroughly  incorporating  these  ingredients.  The 
paste  thus  obtained  is  applied  as  a  thin  layer  to  the  moistened  sur- 
faces of  the  bricks  or  stones  to  be  united.  The  pasty  mortar  soon 
sets  to  the  hard  mass  above  described,  and,  on  continued  exposure  to 
the  air,  it  slowly  absorbs  carbonic  acid  at  its  surface,  and  is  there  con- 
verted into  a.  compact  compound  of  hydrate  and  carbonate  of  calcium. 
The  stone-like  mass  thus  obtained  binds  firmly  together  the  bricks 
or  stones  between  which  it  has  been  interposed.  The  plastering  used 
for  finishing  the  walls  and  ceilings  of  rooms  is  mortar,  to  which  a 
quantity  of  hair  has  been  added  to  increase  its  tenacity  ;  in  drying, 
it  is,  of  course,  subject  to  the  same  chemical  changes  as  ordinary 
mortar. 

422.  Calcium  hydrate,  like  sodium  or  potassium  hydrate, 
exhibits  a  strong  alkaline  reaction  when  tested  with  moistened 
litmus-paper,  arid  exerts  a  corrosive  action  upon  most  organic 
substances ;  hence  it  is  often  called  caustic  lime.  The  value 
of  lime,  as  an  ingredient  of  composts  to  be  used  as  manure, 
appears  to  depend,  in  great  measure,  upon  its  power  of  hasten- 
ing the  decay  and  disintegration  of  organic  matter. 

Exp.  196.  —  Add  a  few  drops  of  water  to  a  small  quantity  of  dry 
calcium  hydrate,  and  rub  it  to  a  paste  between  the  fingers.  It  will 
be  felt  that  the  alkali  acts  upon  the  skin  ;  a  little  of  the  cuticle  is 
really  dissolved. 

Lime  is  important,  also,  from  being  not  only  the  cheapest 
alkali,  but  the  cheapest  of  all  the  bases.  It  is  used  in  the 
manufacture  of  the  caustic  alkalies,  soda  and  potash ;  of  am- 
monia-water and  of  bleaching-powders  ;  as  a  flux  in  many  metal- 
lurgical operations ;  in  the  refining  of  sugar  ;  for  preparing  a 
lime-soap  in  the  manufacture  of  "  stearine "  candles,  and  for 
numberless  other  purposes. 


$  424.1      CALCIUM  SULPHATE. —  PLASTER   OF  PARIS.         245 

0  *  J 

423.  Calcium   sulphate   (CaSO4)    occurs   in   nature   as   the 
mineral  anhydrite.     The  mineral  gypsum  is  a  hydrated  calcium 
sulphate  (CaSO4  -\-  2  H2O).     The  same  hydrated  salt  may  be 
obtained  by  adding  sulphuric  acid,  or  the  solution  of  some  sul- 
phate, to  a  strong  aqueous  solution  of  almost  any  of  the  salts  of 
calcium. 

"When  gypsum  is  heated  moderately  it  is  converted  into  the 
anhydrous  calcium  sulphate,  which  is  often  called  plaster  of 
Paris.  If  the  anhydrous  salt  thus  prepared  be  made  into  a 
-paste  with  water,  and  then  left  to  itself,  it  soon  sets  or  hardens 
into  a  compact,  coherent  mass.  This  solidification  is  a  conse- 
quence of  the  reassumption  by  the  calcium  sulphate  of  the  two 
molecules  of  water  of  crystallization  which  were  driven  off  by 
heat  when  the  substance  was  made  anhydrous. 

On  account  of  this  property,  plaster  of  Paris  is  largely  used 
for  making  casts  of  various  objects.  It  is  also  used  in  the  manu- 
facture of  stucco  and  of  various  imitations  of  marble. 

424.  Ordinary   hydrated    calcium    sulphate    is   soluble   in 
about  400  parts  of  water  at  the  ordinary  temperature.     It  occurs 
in  sea-water  and  also  in  most  well-  and  spring- waters.     Water 
containing  calcium  salts,  such  as  the  carbonate  and  sulphate, 
is  "  hard,"  and  is  not  well  adapted  either  for  washing  or  for 
cooking. 

Exp,  197.  —  Dissolve  a  small  bit  of  the  hard  soap  of  Exp.  Ill 
in  hot  water,  and  add  to  the  solution  an  equal  bulk  of  a  solution  of 
calcium  sulphate.  The  mixture  immediately  becomes  turbid,  and 
after  a  few  moments  there  will  be  formed  a  greasy,  flocculent,  adhe- 
sive scum  upon  the  surface  of  the  liquor.  This  precipitate  is  lime-soap. 

Hard  soap  may  be  regarded  as  essentially  sodium  stearate  ;  on  the 
addition  of  calcium  sulphate  the  metals  calcium  and  sodium  change 
places,  sodium  sulphate  and  calcium  stearate  being  formed  :  the  latter, 
as  has  been  seen,  is  insoluble  in  water.  When  soap  is  added  to  hard 
water,  it  will  neither  produce  any  permanent  froth  nor  cleansing 
effect,  until  the  sulphate,  or  other  lime-salt  present,  has  all  been  de- 
composed ;  with  such  waters,  much  soap  is  consumed  in  removing  the 
calcium  compound,  before  the  proper  detergent  action  of  the  soap 
can  be  brought  into  play. 
20* 


246  CALCIUM  PHOSPHATE.  [§  425. 

425.  Calcium  Phosphate.  —  The  most  important  of  the  va 
rious  calcium  phosphates  is  the  calcium  phosphate   (Ca,jP2O8) 
commonly  called  bone-phosphate,  because  found  in  bones.     It 
is  the  chief  of  the  inorganic  constituents  of  which  the  skeletons 
of  animals  are  composed.      Small  portions  of  it  are  found  in 
most  rocks  and  soils  (§  142),  it  being  a  very  widely  diffused, 
though    nowhere    a   very   abundant    substance.      Considerable 
masses  of  it  have  been  found,  however,  in  Spain,  New  Jersey, 
North  Carolina  and  Canada,  and  it  is  the  principal  ingredient 
of  some  kinds  of  guano.     No  matter  whence  obtained,  it  is  a 
valuable  manure  when  reduced  to  a  fine  powder.     Though  as 
good  as  insoluble  in  water,  it  dissolves  readily  in  acids  and  in 
solutions  of  various  organic  substances. 

When  this  calcium  phosphate  is  treated  with  strong  sulphuric  acid 
there  is  formed  a  soluble  hydrogen  calcium  phosphate  (H4CaP2O8), 
commonly  called  "  superphosphate  of  lime." 

Ca3P208  -f  2  H2S04  =  H4CaP208  -f  2  CaSO4. 

Artificial  fertilizers  are  made  by  thus  treating  ground  bones  with 
sulphuric  acid.  The  reaction  just  given  is  also  one  step  in  the  manu- 
facture of  phosphorus  from  bones. 

In  the  manufacture  of  phosphorus  the  burnt  bones  are  first  treated 
with  sulphuric  acid.  The  soluble  hydrogen  calcium  phosphate 
(H4CaP2O8)  is  filtered  from  the  insoluble  calcium  sulphate,  mixed 
with  charcoal,  dried  and  ignited.  The  following  reaction  takes  place  ; 
a  portion  of  the  phosphorus  is  set  free  and  condensed  under  cold 
water,  while  the  residue  consists  of  a  certain  amount  of  calcium  phos- 
phate identical  in  composition  with  that  originally  contained  in  the 
bone  ash  :  — 

3  H4CaP208  -|-  10  C  =  Ca3P208  -f  4  P  -f  10  CO  -f  6  H2O. 

426.  Calcium    chloride    (CaCl2)   may  be   prepared   by  dis- 
solving chalk  or  marble  in  chlorhydric  acid  (as  in  Exp.  75), 
and  evaporating  the  solution  to  dryness.     When  dried  at  about 
200°,  calcium  chloride  is  left  as  a  porous  mass,  which  is  largely 
employed   in   chemical   laboratories  for   drying   gases    (Appen- 
dix, §  16).     It  absorbs  water  with  great  avidity,  and  is  one  of 
the  most  deliquescent    substances  known.      When  exposed  to 


§  428.]  BARIUM  AND  STRONTIUM.  247 

air  at  the  ordinary  temperature,  it  soon  absorbs  so  much  water 
that  it  dissolves  completely.  At  a  low  red-heat  the  anhydrous 
chloride  melts  to  a  clear  liquid. 

427.  Calcium  hypochlorite  (CaCl2O2),  as  has  been  shown  in 
§  85,  is  a  component  of  the  substance  commonly  called  "  chlo- 
ride of  lime"     This  important  bleaching  agent  is  prepared  by 
passing  chlorine  gas  into  chambers  filled  with  layers  of  finely- 
powdered  slaked-lime.     Chloride  of  lime,,  or  bleaching-powder, 
is  a  dry,  white  powder,  smelling  feebly  of  hypochlorous  acid ; 
when  exposed  to  the  air,  it  slowly  absorbs  carbonic  acid,  and,  at 
the  same  time,  evolves  chlorine  :  hence  its  employment  as  a  dis- 
infecting agent.     If,   instead   of  being  left  to  be  slowly  acted 
upon  by  the  carbonic  acid  of  the  air,  it  be  treated  with  a  dilute 
acid,  —  such  as  vinegar,  —  a  copious  evolution  of  chlorine  will 
immediately  occur.     When  heated,  bleaching-powder  gives  off 
oxygen,  a-nd  calcium  chloride  is  left  as  a  residue. 

Bxp.  188.  — Fill  an  ignition  tube  one-third  full  of  bleaching 
powder,  and  arrange  the  apparatus  so  that  the  gas  may  be  collected 
over  water.  Heat  the  tube,  and  observe  that  the  gas  is  expelled  at  a 
comparatively  low  temperature.  1  grm.  of  bleaching  powder  yields 
40  or  50  c.  c.  of  oxygen  gas. 

STRONTIUM    (sr)    AND    BARIUM    (fia). 

428.  The  metals  strontium  and  barium  closely  resemble  cal- 
cium in   appearance    and   properties.     The    specific  gravity  of 
strontium  is  2.6  ;  that  of  barium  is  4.0.     The  atomic  weight  of 
strontium  is  87.5,  and  that  of  barium  137.     Like  calcium,  stron- 
tium and  barium  are  both  bivalent  elements. 

Most  of  the  compounds  of  strontium  and  barium  are  closely  analo- 
gous to  the  corresponding  compounds  of  calcium.  The  oxides,  per- 
oxides, hydrates,  carbonates,  sulphates,  nitrates,  phosphates,  chlorides, 
sulphides,  etc.,  resemble  in  the  main  the  corresponding  calcium  salts. 
The  hydrates  of  strontium  and  barium  are,  however,  more  readily 
soluble  in  water  than  calcium  hydrate,  while  their  sulphates,  nitrates 
and  chlorides  are  less  soluble  than  those  of  calcium.  Barium  sulphate 
is  almost  absolutely  insoluble  in  water,  and  strontium  sulphate  is  only 
very  slightly  soluble.  Barium  sulphate  is  found  native,  sometimes  in 
considerable  masses,  as  a  very  heavy  white  mineral  called  barytes, 


248  LEAD.— ITS  SEPARATION  FROM  SILVER.       [§  429. 

which,  when  powdered,  is  largely  employed  for  adulterating  white 
lead.  The  name  barium  comes  from  a  Greek  word  meaning  heavy. 
Strontium  salts  are  commonly  prepared  from  the  native  carbonate,  a 
mineral  called  strontianite,  while  the  various  salts  of  barium  are 
obtained  either  from  the  native  carbonate  (witherite),  or  more 
commonly  from  the  sulphate. 

The  colors  imparted  to  the  gas  flames  by  the  compounds  of  cal- 
cium, strontium  and  barium  may  be  illustrated  as  follows  :  — 

Exp.  199.  —  By  means  of  iron  wire,  suspend  three  small  bullets 
of  well-burned  coke  from  a  ring  of  the  iron  stand.  Heat  the  frag- 
ments in  turn  with  the  flame  of  the  gas  lamp,  and  observe  the  slightly 
yellowish  flame  which  will  be  produced  in  each  case  ;  then  moisten 
one  of  the  pieces  of  coke  with  a  solution  of  calcium  chloride,  the 
second  with  a  solution  of  barium  chloride,  and  the  third  with  a  solu- 
tion of  strontium  nitrate,  and  again  heat  them  in  turn  with  the  gas 
flame.  The  calcium  salt  will  impart  a  reddish-yellow  color  to  the 
flame,  the  barium  salt  a  green  color,  and  the  strontium  salt  a  beautiful 
crimson. 

LEAD  (pb). 

429.  Almost  all  the  lead  which  is  employed  in  the  arts  is 
extracted  from  native  lead  sulphide,  PbS,  the  mineral  galena. 
This  substance  is  tolerably  abundant  in  many  localities,  and  is 
often  associated  with  barium  sulphate,  fluor-spar,  quartz  and 
other  common  minerals  ;  it  almost  always  contains  a  small  pro- 
portion of  silver  sulphide. 

Lead  is  a  remarkably  soft  metal,  of  bluish- white  color ;  it 
can  be  readily  cut  with  a  knife,  and  may  even  be  indented  with 
the  finger- nail;  it  soils  paper  upon  which  it  is  rubbed.  Its 
specific  gravity  is  11.4,  and  its  atomic  weight  207.  It  may  be 
drawn  into  wire,  and  beaten  into  sheets,  though,  as  contrasted 
with  most  of  the  other  metals,  it  has  but  little  tenacity.  It 
melts  at  about  325°,  and  may  be  obtained  in  crystals  by  slowly 
cooling  the  molten  metal. 

The  ready  crystallization  of  lead  furnishes  a  very  simple  method  of 
separating  this  metal  from  the  silver  with  which  crude  lead  is  almost 
always  contaminated  as  it  comes  from  the  smelting  furnaces.  When 
melted  argentiferous  lead  is  allowed  to  cool  slowly,  and  is  at  the  same 
time  briskly  stirred,  a  quantity  of  solid  crystalline  grains  separate 


§  431.]       ACTION  OF  AIR  AND   WATER   ON  LEAD.  249 

out  after  a  while,  and  sink  beneath  the  liquid  metal,  whence  they 
may  be  dipped  out  in  colanders.  These  crystals  are  composed  of 
lead,  nearly  free  from  silver,  while  all  but  a  trace  of  the  silver  con- 
tained in  the  original  lead  is  left  in  that  portion  of  the  metal  which 
has  not  yet  solidified  ;  in  a  word,  the  alloy  of  lead  and  silver  melts  at 
a  lower  temperature  than  pure  lead.  By  methodically  remelting  and 
recrystallizing  the  lead  crystals  on  the  one  hand,  and  the  silver  alloy 
on  the  other,  it  has  been  found  profitable  to  extract  the  silver  from 
lead  so  poor  that  it  contained  less  than  one  thousandth  part  its 
weight  of  the  precious  metal.  • 

430.  When  in  thick  masses,  such  as  the  common  sheets  and 
pipes  of  commerce,  lead  is  scarcely  at  all  acted  upon  by  cold  sul- 
phuric acid,  and  is  but  slowly   corroded  by  chlorhydric  acid. 
Both  these  acids  form,  by  their  action  on  the  lead,  difficultly 
soluble  salts ;  and  as  soon  as  a  layer  of  the  salt  has  once  been  de- 
posited upon  the  surface  of  the  metal,  the  latter  is  thereby  pro- 
tected from  further  corrosion.     On  exposure  to  the  air,  lead  soon 
tarnisbes,  owing  to  the  formation  of  a  thin  coating  of  a  lead 
suboxide.     By  the  simultaneous  or  alternate  action  of  water  and 
air,  lead  is  very  rapidly  corroded  in  consequence  of  the  formation 
of  a  lead  hydrate,  which  is  converted  by  the  carbonic  acid  of 
the  air  into  a  carbonate,     All  natural  waters  act  more  or  less  on 
lead.     In  some  cases  the  action  is  so  slight  that  lead  pipes  are 
used  with  safety  for  conveying  the  water ;  in  other  cases  the  use 
of  lead  pipes  is  very  dangerous  on  account  of  the   poisonous 
character  of  the  salts  of  lead. 

431.  Lead  protoxide  (PbO),  commonly  called  litharge,  may 
"be  obtained  as  a  lemon-yellow  powder  by  gently  igniting  the 
nitrate  or  carbonate.     In  the  arts,  litharge  is  prepared  upon  the 
large  scale  by  heating  metallic  lead  in  a  current  of  air ;  the  color 
and  texture  of  the  product  vary  considerably  according  to  the 
temperature  and  other  conditions  at  which  the  litharge  has  been 
prepared. 

Exp.  200.  —  Heat  a  small  fragment  of  lead  upon  charcoal  in  the 
oxidizing  flame  of  the  blowpipe,  and  observe  the  gray  film  of  sub- 
oxide  which  forms  at  first,  and  the  yellow  incrustation  of  litharge 


250  SALT  OF  LEAD.  — CALCIUM  GROUP.  [§432. 

which  is   obtained  subsequently.     The  litharge  may  be  melted  if  a 
strong,  hot  flame  be  thrown  upon  it. 

Other  oxides  of  lead  are  the  peroxide  (PbOa),  a  dark 
brown  powder  formed  by  oxidizing  litharge,  and  red  lead  or 
minium,  which  is  a  compound  of  PbO  and  PbO2  in  varying 
proportions. 

432.  Lead    sulphide    (PbS)    occurs    native   as   the    mineral 
galena.     It  is  also  formed  when  hydrogen  sulphide  is  passed 
into  a  solution  of  a  lead  salt.     The  precipitate  which  forms  in 
this  case  is  black  or  brown,  or  even  red,  if  the  solution  be  dilute. 
On  account  of  the  deep  color,  as  well  as  the  insolubility  of 
this  precipitate,  hydrogen  sulphide  is  often  made  use   of  as  a 
means  of  detecting  lead ;  the  test  is,  in  fact,  so  delicate  that 
solutions  containing  only  a  hundred  thousandth  of  their  weight 
of  metallic  lead  will  assume  a  brown  color  on  being  charged 
with  hydrogen  sulphide. 

433.  Other  Salts  of  Lead.  —  Lead  acetate,  a  soluble,  readily 
crystallizable  salt,  is  much  used  in  the  arts.     It  has  a  sweet, 
astringent  taste,  whence  the  name  sugar  of  lead.     Like  other 
lead  salts,  it  is  highly  poisonous.     Lead  carbonate  (PbCO3), 
or  rather  compounds  of  the  carbonate  and  hydrate  in  varying 
proportions,  are  used  to  an  enormous  extent  as  a  white  paint, 
under  the  general  name  of  white  lead.     Lead  silicate  is  of 
interest  from  being  an  important  ingredient  of  flint  glass ;   a 
certain  proportion  of  it  renders  glass  lustrous  and  very  beauti- 
ful.     Such  glass  is,  however,  soft  and  easily  fusible.      It  is, 
moreover,  rather  easily  acted  upon  by  alkalies,  acids  and  other 
chemical  agents,  and  is  hence  not  well  suited  for  use  in  the 
chemical  laboratory. 

434.  In  many  points  of  chemical  behavior  the  compounds  of 
lead  resemble  more  or  less  clearly  the  corresponding  compounds 
of  barium,  strontium  and  calcium.     It  is,  moreover,  bivalent, 
like  the  elements  in  question.     Lead  is,  therefore,  classed  as  a 
member  of  the  calcium  group,  although,  as  in  the  case  with 
fluorine  in  the  chlorine  group,  it  differs  in  some  respects  from 
the  other  members  of  the  family.     The  specific  gravity  of  lead 
is  11.4,  and  its  atomic  weight  207. 


§437.]  THE  METAL  MAGNESIUM.  251 

CHAPTEE  XXV. 
MAGNESIUM,  ZINC,  AND  CADMIUM. 

MAGNESIUM    (Mg). 

435.  The  compounds  of  magnesium  are  found*  widely  dif- 
fused, and  rather  abundantly,  in  nature.     The  bitter  taste  of  sea- 
water  and  of  some  mineral  waters  is  due  to  the  presence  of  mag- 
nesium salts,  while  magnesium  silicate  and  carbonate  are  con- 
tained in  a  variety  of  minerals,  and  in  such  common  rocks  as 
dolomite,  serpentine,  soapstone  and  talc. 

436.  Metallic  magnesium  may  be  prepared  by  heating  an- 
hydrous magnesium   chloride    with   metallic  sodium,  and  sub- 
sequently   dissolving   out   in    cold  water   the   sodium  chloride 
which   results   from   the   reaction.     Magnesium   is   a  lustrous 
metal,  as  white  as  tin ;  its  symbol  is  Mg  and  its  atomic  weight 
24.     It  does   not   tarnish  in  dry  air,  though  in  damp  air  it 
soon  becomes  covered  with  a  film  of  magnesium  hydrate.     Cold 
water  acts  on   magnesium  only  slowly ;  hot  water  acts  more 
rapidly,   magnesium    oxide  being  formed  and  hydrogen  being 
set  free.     The  metal  dissolves  readily  in  almost  any  acid  with 
evolution  of  hydrogen.     It  melts  at  a  low  red  heat,  and  vola- 
tilizes at  higher  temperatures  ;  it  may  be  readily  distilled  at  a 
bright   red   heat.     When   heated  strongly  in  the  air  it  takes 
fire    and    burns    with  a  bluish- white   light  of  great   brilliancy 
and  high  actinic  power.     The  metal  is  employed  by  photogra- 
phers   for   illuminating    caverns    and    other  places   into  which 
sunlight  cannot  penetrate,    and  in  cloudy  weather  it  is  even 
used  by  them  as  a  substitute  for  daylight.     The  metal  can  be 
pressed   into   wire    or   into   thin   ribbons,   and   a   considerable 
quantity  of  it  is  now  used  in  both  these  forms  for  purposes  of 
illumination. 

437.  Magnesium  Oxide  or  Magnesia  (MgO).  —  There  is  but 
one  compound  of  magnesium  and  oxygen ;  it  is  obtained  as  a 
white  amorphous  powder  when  magnesium  is  burnt  in  the  air, 


252  MAGNESIUM  SALTS.  — ORES  OF  ZINC.          [§  438. 

or  it  may  be  prepared  by  igniting  the  carbonate,  chloride  or 
nitrate. 

Exp.  201.  —  Roll  10  or  12  c.  m.  of  magnesium  wire  or  thin  rib- 
bon into  a  coil  around  a  small  pencil ;  withdraw  the  pencil  and  place 
in  its  stead  a  piece  of  iron  wire  or  a  knitting-needle ;  holding  this  wire 
horizontally,  apply  a  lighted  match  to  the  end  of  the  magnesium  coil  ; 
the  magnesiiun  will  burn  to  the  white  oxide  which  coheres  in  an  im- 
perfect coil,  clinging  to  the  iron  wire.  A  portion  of  the  oxide  goes  off 
as  white  smoke. 

The  oxide  is  tasteless  and  odorless.  It  is  altogether  infusible 
at  temperatures  short  of  that  of  the  oxy-hydrogen  flame.  Very 
excellent  crucibles  for  scientific  purposes  are  prepared  by  com- 
pressing magnesium  oxide  into  suitable  forms. 

438.  Salts  of  Magnesium,  —  Magnesium  chloride  (MgCl2) 
is  found  in  sea-water  and  many  saline  springs.     Magnesium  sul- 
phate (MgSO4),   or  rather  the  hydrated  compound  (MgSO4  4- 
7  H2O),  is  known  as  Epsom  salts  on  account  of  its  occurrence 
in  a  mineral  spring  at  Epsom,   England.     It  occurs  in  other 
springs,  and  is  made  artificially  from  various  native  minerals 
containing  magnesium.     It  is  a  colorless  crystalline  salt,  readily 
soluble   in   water,    and    having   a   bitter    taste.       It    is   much 
used   in  medicine.      Magnesium    carbonate   (MgCO3)   occurs 
native  as  the  mineral  magnesite.     The  magnesia  alba  of  the 
shops  is  a  varying  mixture  of   magnesium  carbonate   and  hy- 
drate,  and  is  prepared  by  adding  sodium  carbonate  to  a  hot 
solution  of  magnesium  sulphate. 

ZINC  (zn). 

439.  Zinc  does  not  occur  in  nature  in  the  metallic  state,  but 
in  combination  with  other  elements  such  as  oxygen  (red  oxide 
of  zinc)  and  sulphur  (zinc  sulphide,  or  blende) ;  the  carbonate 
and  the  silicate  of  zinc  are  also  native  minerals. 

Zinc  is  a  bluish-white  metal  of  crystalline  texture,  brittle  at 
the  ordinary  temperature,  and  also  when  heated  above  200°,  but 
at  a  temperature  of  about  130°  or  140°  it  may  easily  be  rolled 
out  or  hammered  into  sheets.  The  metal  melts  at  425°,,  and 


§  440.]  COMBUSTION  OF  ZINC.  253 

boils  at  a  bright  red  heat  :  in  presence  of  air  the  red-hot  metal 
takes  fire  and  burns  with  a  brilliant  bluish-white  light  and 
formation  of  a  dense  cloud  of  white  oxide  of  zinc. 

If  a  strip  of  thin  sheet  zinc  be  held  in  the  flame  of  the  gas  lamp, 
it  can  readily  be  burned  to  oxide.  The  experiment  succeeds  best 
with  zinc  leaf,  which  instantly  burns  with  a  vivid  flame  and  forma- 
tion of  floating  flocks  of  the  white  oxide.  In  oxygen  gas,  zinc  burns 
with  peculiar  brilliancy. 

Exp.  202.  —  Mix  intimately  in  a  mortar  20  grms.  of  dry  granu- 
lated zinc  (or  zinc  dust,  if  it  can  be  obtained)  and  40  grms.  of  crude 
saltpetre  ;  heat  to  redness  a  small  Hessian  crucible  in  an  anthracite 
fire  ;  remove  the  crucible  from  the  fire,  and  place  it  in  such  position 
that  any  fumes  which  may  subsequently  be  evolved  from  it  shall  be 
drawn  into  the  chimney.  By  means  of  a  spoon  or  ladle,  project  into 
the  red-hot  crucible  the  mixture  of  zinc  and  saltpetre,  taking  care  to 
stand  away  as  far  as  possible  from  the  crucible.  The  greater  part  of 
the  metal  will  burn  fiercely,  at  the  expense  of  the  oxygen  in  the  salt- 
petre, though  a  portion  of  it  will  be  volatilized  by  the  intense  heat  of 
combustion  and  converted  into  zinc  oxide  in  the  air.  The  residue  in 
the  crucible  is  a  soluble  compound  known  as  potassium  zincate. 

Granulated  zinc  is  much  used  in  chemical  laboratories,  for  a 
variety  of  purposes,  but  particularly  for  preparing  hydrogen  (§  35). 
It  may  be  prepared  by  melting  the  zinc  in  a  Hessian  crucible  and 
heating  the  melted  metal  nearly  to  redness.  The  crucible  is  then 
removed  from  the  fire  and  its  contents  poured,  in  a  thin  stream,  from 
a  height  of  6  or  8  feet  into  a  vessel  of  cold  water.  This  process  of 
granulation  or  feathering  may  be  conveniently  applied  to  any  of  the 
other  easily  fusible  metals,  such  as  bismuth,  lead  or  tin,  when  they 
are  required  in  a  finely  divided  condition. 

In  the  manufacture  of  zinc  a  quantity  of  the  vaporized  metal  is 
condensed  in  a  very  fine  state  of  division  corresponding  to  the  "  flow- 
ers of  sulphur."  This  zinc  dust  (which  contains,  also,  some  zinc  oxide) 
is  already  used  to  a  considerable  extent  in  Europe  in  indigo-dyeing  in 
the  manner  illustrated  by  Exp.  159,  but  has  not  yet  become  an  ordi- 
nary article  of  commerce  in  this  country.  It  is  a  very  convenient 
form  of  the  metal  for  many  experimental  purposes. 

440.    Zinc  is  not  much  acted  upon  either  by  moist  or  dry  air, 
at  the  ordinary  temperature,  as  it  soon  tarnishes  arid  becomes 
covered  with  a  thin  film  of  a  basic  carbonate  of  zinc,  which 
22 


254 


THE  GALVANIC  CURRENT. 


[§  441. 


adheres  closely  to  the  metal,  and  protects  it  from  further  change. 
Owing  to  this  durability,  the  metal  is  much  used  in  the  form 
of  sheets.  Sheet  iron  and  iron  wire  also  are  often  covered  with 
a  protecting  coating  of  zinc,  and  are  then  said  —  most  im- 
properly —  to  be  galvanized.  Zinc  forms  several  valuable 
alloys ;  brass  is  an  alloy  of  zinc  and  copper,  and  German  silver 
is  a  brass  whitened  by  the  admixture  of  a  small  proportion  of 
nickel.  The  specific  gravity  of  zinc  varies  from  6.8  to  7.3;  its 
atomic  weight  is  65. 

441.  Zinc  is  readily  attacked  and  dissolved  by  acids,  in  most 
instances  with  evolution  of  hydrogen.  The  chemical  action 
of  dilute  acids  upon  zinc  is  a  very  common  source  of  that 
peculiar  mode  of  force  called  a  galvanic  current.  There 
are  few,  if  any,  chemical  reactions  which  cannot  be  made  to 
produce  electricity,  and  in  general,  the  more  powerful  the  chemi- 
cal action,  the  more  powerful  is  the  electrical  action  which 
results. 

Exp.  203.  —  Solder  a  piece  of  stout  copper  wire  to  one  end  of  a 
strip  of  sheet  zinc,  4  c.  m.  wide  by  10  c.  m.  long.  The  soldering  will 
be  readily  effected  by  rubbing  the  zinc  and  the  wire  in  the  vicinity 
of  the  proposed  place  of  contact,  with  a  strong  solution  of  zinc 
chloride,  before  applying  the  melted  solder.  In  the  same  way,  sol- 
der a  similar  wire  to  a  like  strip  of  bright  sheet  copper.  Place  the 
strips  of  zinc  and  copper  in  a  vessel  filled  with  water,  acidulated  with 

1-12  to  1-lOth  its  volume  of  sul- 
phuric acid  in  such  a  way  that  the 
two  strips  shall  not  touch  each 
other  either  within  or  without  the 
liquid.  As  long  as  the  wires  com- 
ing from  the  strips  of  metal  do  not 
touch  each  other,  the  copper  re- 
mains quiescent,  while  the  zinc  is 
attacked,  and  bubbles  of  gas  rise 
from  its  surface  ;  but  if  the  two 
copper  wires  are  brought  into  close 
contact,  by  means  of  a  binding- 
screw,  or  by  the  application  of  solder,  the  following  phenomena  occur  : 
1st.  Minute  bubbles  of  hydrogen  gas  will  be  evolved  from  the  surface 


Fig.  73. 


§  442.]  THE  LEAD-TREE.  255 

of  the  copper  plate.  2d.  The  zinc  dissolves  more  rapidly  than 
before,  and  at  the  close  of  the  experiment,  zinc  sulphate  may  be 
recovered  from  the  liquid  in  the  beaker.  3d.  This  transfer  of  the 
hydrogen  from  the  zinc  to  the  copper  instantly  ceases,  if  the  contact 
between  the  wires  is  destroyed.  4th.  If  the  two  wires  be  connected 
with  the  two  ends  of  the  coil  of  wire  which  surrounds  the  magnetic 
needle  of  the  common  galvanometer,  the  deflection  of  the  suspended 
needle  will  demonstrate  the  fact  that  an  electric  current  is  passing 
through  the  wires  from  one  plate  of  metal  to  the  other. 

This  experiment  well  illustrates  the  principle  on  which  a  large 
class  of  batteries  employed  in  telegraphing  and  in  electro-metal- 
lurgy are  constructed  and  worked,  except  that  the  corrosion  of 
the  zinc  is  generally  hindered  by  coating  it  with  mercury. 

442.  When  zinc  is  immersed  in  the  solution  of  a  lead  salt, 
such  as  the  nitrate  or  acetate,  zinc  dissolves,  and  lead  is  deposited 
in  the  metallic  state  :  PbN2O0  -f-  Zn  =  ZnN2O6  -f-  Pb. 

Exp.  204. — Dissolve  10  grms.  of  lead  acetate  in  250  c.  c.  of 
water,  add  a  few  drops  of  acetic  acid  in  order  to  dissolve  the  cloudy 
precipitate  of  lead  carbonate,  which  is  formed  from  the  Fi« 
carbonic  acid  in  the  water,  pour  the  solution  into  a  wide- 
mouthed  bottle  and  suspend  in  it  a  strip  of  sheet  zinc. 
The  zinc  will  soon  be  covered  with  a  brilliant  coating  of 
crystalline  spangles  of  metallic  lead,  and  this  crystalline 
vegetation,  which  is  known  as  the  lead-tree,  will  continue 
to  grow  until  all  the  lead  has  been  deposited  from  the 
solution  ;  the  latter  will  now  contain  nothing  but  zinc  acetate. 

If,  in  this  experiment,  the  piece  of  zinc  be  weighed  before  and  after 
its  immersion  in  the  lead  acetate,  and  if  the  precipitated  lead  be  also 
weighed,  it  will  be  found  that  the  weight  of  the  lead  obtained  is  to 
the  weight  of  the  zinc  dissolved  very  nearly  as  207  is  to  65, —  that  is, 
as  the  atomic  weights  of  lead  and  zinc  respectively.  This  experiment 
is  interesting  as  illustrating  the  general  law  of  the  replacement  of  one 
metal  by  another  according  to  a  fixed  proportion  ;  when  the  quan- 
tivalence  (see  §  74)  of  the  two  metals  is  the  same,  this  proportion  is 
the  ratio  of  the  atomic  weights  ;  when  the  quantivalence  is  different, 
the  proportion  is  some  multiple  of  this  ratio.  Thus,  in  the  foregoing 
experiment,  for  every  atom  of  lead  precipitated  an  atom  of  zinc  was 
dissolved.  In  the  similar  case  represented  by  the  following  equation 
one  atom  of  zinc  takes  the  place  of  two  atoms  of  silver  :  — 
2  AgN08  -f  Zn  =  ZnN206  -f  2  Ag. 


256 


ELECTRO-CHEMICAL   RELATIONS  OF 


[§  443. 


443.   Electro-chemical  Relations    of  the  Elements.  —  Other 
substances,  besides  the   zinc  and  copper  of   Exp.  203,  if  brought 
into  contact  in  a  liquid  capable  of  affecting  them  unequally,  exhibit 
similar  electrical  phenomena.     It  is  necessary  that 
the  substances  should  both  be  conductors  of  elec-     Negative  End — . 
tricity,  and  that  the  liquid  should   contain   some     OXYGEN. 
compound  capable  of  such  decomposition  that  there     SULPHUR. 
shall  be  formed  a  new  compound  containing  one     NITROGEN. 
of  the  substances  immersed  in  the  liquid.     When     FLUORINE. 
the  two  substances,  as  in  Exp.  203.  are  connected     CHLORINE. 
by  means  of  a  copper  wire,  a  current  of  electricity     BROMINE. 
passes  along  the  wire  in  each  direction  ;  the  cur-     IODINE. 
rent  which  passes  from  the  zinc  to  the  copper  in     PHOSPHORUS. 
the  liquid,  and  from  the  copper  to  the  zinc  in  the     ARSENIC. 
air,  is  called  the  positive  current,  and  under  such     BO-RON. 
conditions  the  zinc  is  said  to  be  positive  with  refer-     CARBON. 
ence  to  the  copper.  ANTIMONY. 

When  the  wire  which  connects  the  two  plates     SILICON. 
is  cut,  the  flow  of  electricity  ceases  ;  but  if  the     HYDROGEN. 
two  extremities  of  the  wires  be  immersed  in  some 
conducting  liquid,  the  flow  is  re-established.     In     GOLD. 
many  cases  the  passage  of  the  current  through  a    PLATINUM. 
liquid  affects  its  decomposition.     Th«  two  extrem-     SILVER. 
ities  of  the  wires  are  called  poles  ;  that  connected     MERCURY. 
with  the  negative  plate  is  called  the  po^tive»pole,     COPPER. 
and  that  connected  with  the  positive  plate  is  called     TIN. 
the  negative  pole.     If  the  poles  of  a  galvanic  bat-     LEAD. 
tery  be  immersed  in  a  solution  of  zinc  chloride    COBALT. 
(ZnCl3),  for  example,  this  salt  is  decomposed  by     NICKEL. 
the  action  of  the  electrical  current ;  the  atoms  of    IRON. 
zinc  go  to  the  negative  pole,  and  hence  are  called     ZINC. 
positive,  with  reference  to  the  atoms  of  chlorine,     MANGANESE. 
which  are  called  negative,  because  they  go  to  the     ALUMINUM. 
positive  pole.     With  reference  to  other  metals,  as     MAGNESIUM. 
to  magnesium,  for  instance,  zinc  is  negative.     The     CALCIUM. 
terms  positive  and  negative  are  thus  seen  to   be     SODIUM. 
merely  relative,  and  under  certain  circumstances     POTASSIUM. 
the  relation  of  one  element  to  another  may  be  di-     Positive  End  -J-. 
rectly  reversed. 

It  is  possible  to  arrange  the  chemical  elements  according  to  their 
electro-chemical  characters,  as  ordinarily  exhibited,  so  that  each  ele- 


§  445.]       THE  ELEMENTS. —CADMIUM  AND   INDIUM.         257 

ment  in  the  series  will  be  positive  to  any  element  placed  above  it,  and 
negative  to  any  one  given  below  it.  On  page  256  the  elements  are  so 
arranged.  Speaking  somewhat  loosely,  all  the  elements  which  in  this 
list  precede  gold  are  negative,  while  gold  and  the  elements  which  fol- 
low it  are  positive.  The  negative  elements  are  spoken  of  collectively 
as  the  non -metallic  elements,  while  the  positive  are  known  as  the 
metallic  elements.* 

The  property  which  one  metal  possesses  of  replacing  another  in 
its  salts,  as  illustrated  by  Exp.  204,  is  an  exhibition  of  this  same 
relation.  Metallic  copper  may  be  thrown  down  from  a  solution  of 
one  of  its  salts  by  the  introduction  of  metallic  iron  or  zinc  ;  a  little 
metallic  mercury  put  into  a  solution  of  silver  nitrate  will  cause  the 
formation  of  a  silver-tree.  In  these  cases  the  metal  which  goes  into 
solution  is  said  to  be  electro-positive  to  the  metal  which  is  precipitated, 
and  the  latter  is  electro-negative  to  the  former. 

444.  Salts  of  Zinc, —Zinc   oxide  (ZnO)  is  formed  when 
metallic  zinc  is  burned  in  the  air,  and  may  also  be  prepared 
by  igniting  the  carbonate.     Under  the   name  of  zinc  white, 
it   is  somewhat  largely  employed  as  a  white  paint.      It  dis- 
solves  readily   in   acids.      Zinc   chloride   (ZnCi,)   is  a  white, 
soluble,  deliquescent  substance,  formed   by  dissolving  zinc   in 
chlorhydric   acid.     It   is   used   for  preserving   timber,    also   in 
soldering  to  cleanse  the  surface  of  the  metal.     Zinc  sulphate 
(ZnSO4),  or  rather  the  hydratecl  compound  (ZnSO4  -}-  7  H2O), 
known  as  white  vitriol,  is  used  to  a  certain  extent  in  medicine, 
and  also  in  the  arts. 

CADMIUM  (Cd). 

445.  Cadmium   is  a  comparatively  rare  metal,  found  associated 
with  zinc  in  nature  ;  it  is  remarkably  similar  to  zinc  in  its  chemical 
relations.     It  is  a  bluish- white  lustrous  metal,  tarnishing  somewhat 
when  exposed  to  the  air.     It  melts  and  volatilizes  at  temperatures 
below  redness.     Heated  in  the  air,  it  takes  fire  and  burns  to  a  brown 
oxide.     Cadmium  sulphide  is  of  a  bright  yellow  color,  .and  has  been 
used  as  a  pigment. 

*  See  in  this  connection  some  additional  statements  on  page  293. 
22* 


258  PROPERTIES  OF  ALUMINUM.  [§  446. 


CHAPTER  XXVI. 

ALUMINUM,    GLUCINUM,    CHROMIUM,    MANGANESE,    IKON, 
COBALT  AND  NICKEL. 

ALUMINUM    (A!.) 

446.  Aluminum  is  perhaps  the  most  abundant  element  upon 
the  earth's  surface,  next  to  oxygen  and  silicon.  It  is  the 
most  abundant  of  all  the  metals,  as  much  as  a  twelfth  of  the 
solid  crust  of  the  globe  being  composed  of  it.  It  occurs 
in  enormous  quantities  in  combination  with  oxygen  and  sili- 
con, in  most  rocks  and  soils.  It  is  contained  in  clay,  marl 
and  slate,  as  well  as  in  feldspar,  mica  and  many  other  common 
minerals. 

Although  the  compounds  of  aluminum  are  so  abundant,  no 
cheap  method  of  obtaining  the  metal  itself  has  yet  been  de- 
vised. For  this  reason  it  cannot  be  applied  to  many  uses  for 
which  it  is  otherwise  well  suited.  It  is  generally  prepared  by 
heating  metallic  sodium  either  with  chloride  or  fluoride  of  alu- 
minum, or  with  a  double  chloride  or  fluoride  of  aluminum  and 
sodium. 

44*7.  Aluminum  is  a  bluish-white  metal,  of  remarkable  light- 
ness. Its  specific  gravity,  2.56,  is  about  the  same  as  that  of 
porcelain,  and  only  about  a  quarter  of  that  of  silver.  The 
metal  is  malleable,  ductile  and  tenacious,  and  may  be  beaten 
into  thin  sheets,  like  gold  and  silver,  and  drawn  into  fine 
wire.  It  is  remarkably  sonorous  :  a  bar  of  it  suspended  by  a 
wire  rings  with  a  clear  musical  note  on  being  struck.  Alumi- 
num-bronze, an  alloy  of  90  parts  copper  and  10  parts  alumi- 
num, is  exceedingly  hard,  very  malleable,  as  tenacious  as  steel, 
of  a  beautiful  golden  color,  and  susceptible  of  being  highly 
polished. 

448.  Aluminum  oxide,  or  alumina  (A12O3),  occurs  native,  as 
the  minerals  corundum,  ruby  and  sapphire.  Emery  is  impure 
aluminum  oxide. 


§  449.]  ALUMINUM  HYDRATE.  259 

Aluminum  hydrate  (A12H6O6)  may  be  obtained  as  a  gelat- 
inous, flocculent  precipitate,  by  adding  ammonia-water  to  the 
solution  of  an  aluminum  salt.  The  hydrate  dissolves  readily  in 
acids  forming  aluminum  salts  ;  it  also  dissolves  in  caustic  alka- 
lies forming  a  class  of  salts  called  aluminates. 

Exp.  205.  —  Heat  a  small  fragment  of  aluminum  sulphate  (com- 
mon alum  will  answer  equally  well)  with  water  in  a  test-tube  until  it 
has  completely  dissolved,  pour  half  the  solution  into  another  tube,  and 
add  to  it,  drop  by  drop,  ammonia- water,  until  the  odor  of  ammonia 
persists  after  the  mixture  has  been  thoroughly  shaken.  Aluminum 
hydrate  will  be  precipitated  in  accordance  with  the  reaction  :  — 

A13  3  (BO,)  -|-  6  (NHJHO  =  A12H6O6  +  3  (NH4)2SO4. 

Put  two  or  three  drops  of  the  moist  aluminum  hydrate  into 
another  test-tube  and  cover  them  with  ammonia- water ;  no  clear 
solution  will  be  obtained,  for  aluminum  hydrate  is  but  slightly  soluble 
in  ammonia- water. 

Put  two  or  three  drops  of  the  moist  aluminum  hydrate  into  still 
another  test-tube,  and  cover  them  with  a  solution  of  sodium  hydrate  ; 
the  precipitate  will  dissolve  immediately ;  sodium  aluminate  is  formed, 
and  this  salt  is  easily  soluble. 

Exp.  206.  — Take  another  portion  of  the  clear  solution  of  alumi- 
num sulphate  prepared  in  Exp.  205,  and  add  to  it,  drop  by  drop,  a 
dilute  solution  of  caustic  soda.  A  precipitate  will  soon  fall,  as  in 
Exp.  205,  and  if  no  excess  of  sodium  hydrate  were  added,  this  pre- 
cipitate would  remain  undissolved,  but  on  adding  more  of  the  soda 
solution  the  precipitate  dissolves  at  once,  with  formation  of  sodium 
aluminate  (Na2Al2O4). 

449.  Aluminum  hydrate  combines  readily  with  many  organic 
coloring-matters,  forming  compounds  insoluble  in  water. 

Exp.  207. — Take  a  small  quantity  of  the  solution  of  cochineal 
prepared  in  Exp.  154,  add  to  it  an  equal  bulk  of  a  solution  of  alu- 
minum sulphate  (or  of  common  alum),  and  then  add  to  the  mixture 
ammonia- water,  as  in  Exp.  205.  A  colored  precipitate,  consisting  of 
aluminum  hydrate  and  of  the  coloring  matter  of  the  cochineal,  will 
be  thrown  down  ;  it  is  the  substance  called  carmine-lake.  Similar 
precipitates  may  be  prepared  by  substituting  almost  any  other  organic 
coloring  matter  for  the  cochineal  of  this  experiment.  Precipitates 
thus  formed  by  the  union  of  a  metallic  hydrate  and  a  coloring 
matter  are  classed  as  lakes. 


260  USE  OF  MORDANTS  IN  DYEING.  [§  450. 

450.  Mordants.  —  The  fibre  of   cotton,   when   impregnated 
with  alumina,  can  be  made  to  retain  colors  which  the  cotton 
itself  has  no  power  to  hold,  Exp.  156,  §  339 :  hence  the  use  of 
aluminum   salts  as  mordants   in.   dyeing.     In   fact,    mere   im- 
mersion in  a  solution  of  a  salt  of  aluminum  suffices  to  make  a 
great  difference  in  the  amount  of  coloring  matter  taken  up  by 
cotton.     An  acetate  of  aluminum  is  much  employed  in  dyeing, 
because  when  exposed  to  the  air  on  the  cloth  it  is  partly  decom- 
posed, a  certain  amount  of  acetic  acid  is  set  free  and  volatilized, 
leaving  the  fibres  impregnated  with  aluminum  hydrate  or  oxide. 

Exp.  208.  —  Prepare  an  acetate  of  aluminum  as  follows  :  —  Dis- 
solve 6  grms.  of  sugar  of  lead  (lead  acetate)  in  8  c.  c.  of  hot  water  ; 
also  dissolve  8  grms.  of  common  alum  in  12  c.  c.  of  hot  water ;  mix 
the  two  solutions  and  filter  off  the  insoluble  lead  sulphate  which  is 
formed.  In  the  solution  thus  prepared,  soak  a  piece  of  cotton  cloth, 
and  then  hang  it  up  in  a  moist  and  warm  atmosphere  for  several  days< 
Treat  this  cloth,  as  well  as  a  piece  of  ordinary  cotton  of  the  same  size, 
with  a  solution  of  logwood  as  described  in  Exps.  156,  157,  and  observe 
the  difference  in  the  amount  of  color  imparted  to  the  fabric. 

t)ther  oxides  or  hydrates  besides  the  aluminum  hydrate  are  used 
as  mordants.  An  acetate  of  iron  made  by  dissolving  scraps  of  iron 
in  the  crude  pyroligneous  acid  obtained  by  the  destructive  distillation 
of  wood  (§  238)  is  much  used  by  dyers  ;  salts  of  tin,  of  chromium  and 
of  other  elements  are  employed  to  a  greater  or  less  extent. 

451.  Aluminum  sulphate  (A10  3  (SO4))  is  prepared  by  treat- 
ing hot  roasted  clay,  which  is  an  aluminum  silicate,  with  sul- 
phuric  acid.     The  mixture  of   aluminum   sulphate   and   silica 
obtained  is  called  alum-cake,  and  from  it  the  aluminum  sul- 
phate can  be  obtained  by  treating  with  water,  which  dissolves 
the  aluminum  sulphate  and  leaves  the  silica  behind.     Aluminum 
sulphate  is  employed  as  the  source  of  the  various  compounds  of 
aluminum  used  in  dyeing  and  calico-printing.  * 

452.  Alums. — Potassium  alum  is  an  aluminum  potassium 
sulphate  crystallizing  in  sharply  defined  crystals.     Its  composi- 
tion is  represented  by  the  formula  Al^S,  4  (SO4)  -f-  24  H2O.     It 
is  known  as  common  alum,  although  of  late  years  ammonium 


§456.]         CLAY,  EARTHENWARE,  AND   PORCELAIN.  261 

alum  has  to  a  considerable  extent  taken  its  place.     The  formula 
of  ammonium  alum  is  A12  (NH4)2  4  (BO4)  -\-  24  H2Q 

453.  Aluminum    Silicates.  —  Of   all    the    aluminum    com- 
pounds the  silicates  are  by  far  the  most  important.     Clay  in 
all  its  varieties  is  a  hydrated  aluminum  silicate,  usually  mixed 
with  an  excess  of  silica,  besides  other  impurities  derived  from 
the  rocks  from  whose  decomposition  the  clay  itself  has  been 
formed.     Clay  is  remarkable  on  account  of  its  plasticity  when 
moist,  of  the  facility  with  which  it  is  converted  into  stone-like 
masses   when   strongly   heated,    and   of    its   infusibility   when 
pure. 

Earthenware,  bricks,  and  ordinary  pottery  are  made  from  common 
clay,  by  mixing  the  clay  with  water  enough  to  form  a  plastic  paste, 
which  is  then  moulded  into  any  desired  form,  dried  and  intensely 
ignited.  The  red  color  of  certain  varieties  of  ware  is  due  to  the  iron 
oxide  they  contain.  Porcelain  is  made  from  a  very  pure  clay  (kaolin). 
The  glaze  on  articles  of  pottery  is  made  by  coating  them  with  an 
easily  fusible  substance,  such  as  a  mixture  of  litharge  and  clay,  or  in 
the  case  of  porcelain  finely  ground  feldspar,  and  subjecting  them 
thus  coated  to  high  heat.  Ordinary  stone- ware  is  glazed  by  throwing 
common  salt  into  the  kiln.  The  salt  volatilizes  and  coming  in  contact 
with  the  heated  ware  it  is  decomposed,  and  a  fusible  silicate  results 
which  renders  the  articles  impervious  to  moisture. 

GLUCINTJM  (Gl)  and  INDIUM'  (in). 

454.  Glucinum  is  a  rather  rare  metal,  found,  together  with  alumi- 
num, in  the  emerald,  in  beryl  and  in  a  few  other  minerals.      It 
closely  resembles  aluminum  in  its  chemical  and  physical  properties. 
The  atomic  weight  of  glucinum  is  14  ;  its  symbol  is  Gl. 

455.  Indium  is  a  rare  metal,  found  associated  with  zinc  in  certain 
ores,  and  was  discovered  by  means  of  spectrum  analysis.     It  is  a  soft 
white  metal.     Its  atomic  weight  is  113.4  ;  its  symbol  In. 

CHROMIUM  (Cr). 

456.  The  chief  ore  of  chromium   is   a   compound   of  iron, 
chromium,  and  oxygen  (PeCr2O4)  called  chrome  iron-ore.    The 

compounds  of  chromium  are  somewhat  extensively  employed  in 
the  arts, 


262  SALTS  OF  CHROMIUM.— MANGANESE.          [§  457. 

457.  Chromium   sesquioxide  (Cr2O3)  prepared   by   igniting 
the  hydrate  (Cr2H6O6),  is  a  green  powder  somewhat  used  as  a 
pigment.     The  hydrate  may  be  obtained  by  adding  ammonia- 
water  to  a  solution  of  a  salt  of  chromium.     It  forms  a  bulky 
green  precipitate. 

458.  Chromium  sulphate  (Cr2  3  (SO4))  is  sometimes  prepared 
in  the  pure  state ;  generally,  however,  it  is  prepared  in  combina- 
tion with  potassium  (or  ammonium)  sulphate  forming  chrome 
alum,  a  beautiful  violet  crystalline  salt.     The  formula  of  ordi- 
nary chrome  alum  is  Cr^  4  (SO4)  -|-  24  H2O. 

Exp.  209.  —  Dissolve  15  grins,  of  powdered  potassium  bichro- 
mate in  100  c.  c.  of  warm  water  ;  cool  the  solution,  and  then  add  to 
it  25  grms.  of  concentrated  sulphuric  acid  ;  cool  the  liquor  again,  and 
pour  it  into  a  porcelain  dish,  surrounded  with  cold  water  ;  slowly  stir 
into  the  mixture  6  grms.  of  alcohol,  and  set  the  whole  aside.  In  the 
course  of  24  hours,  the  bottom  of  the  dish  will  become  covered  with 
well-defined,  octahedral  crystals  of  chrome  alum. 

In  this  experiment  the  chromic  acid  which  is  set  free  by  the 
sulphuric  acid  gives  up  a  part  of  its  oxygen  to  the  alcohol,  and  is 
converted  into  chromium  sulphate,  which  unites  with  the  potassium 
sulphate  to  form  chrome  alum  :  the  alcohol  is  oxidized  in  part  to 
aldehyde  (§  235)  (the  peculiar  odor  of  which  is  distinctly  perceived) 
and  partly  to  acetic  acid. 

459.  Chromic  anhydride  (CrO3)  may  be  obtained  by  treating 
potassium  bichromate  with  sulphuric  acid.     The  chromic  anhy- 
dride separates  in  red  crystals,  which  dissolve  in  water  with 
formation  of  chromic  acid  (H2CrO4).     Several  of  the  chromates 
find  application  in  the  arts,  as  the  normal  potassium  chromate 
(K2CrO4),   the  potassium  bichromate   (K2Cr2O7  =  K2CrO4,CrO,) 
and  the  lead  chromates. 

MANGANESE    (nn). 

460.  Manganese  is  a  grayish-white,  hard,  brittle  metal,  the 
principal  ore  of  which  is  the  binoxide  (MnO2),  which  has  al- 
ready been  employed  in  the   generation   of   oxygen  (Exp,  4, 
§  12)  and   of  chlorine  (Exp.  30,  §  78).     The  residue   in   the 
latter   case   consisted   of  manganese  chloride,   which   may  be 


§  461.]       POTASSIUM  PERMANGANATE  OXIDIZES.  263 

obtained  in  pink  crystals  (MnCl2  +  4  H2O)  by  filtering  the 
liquid  left  in  the  flask  and  evaporating  the  solution  until  it 
crystallizes. 

There  are  several  oxides  of  manganese  besides  the  binoxide. 

461.  Manganic  anhydride  (MnO3)  and  manganic  acid 
(H2MnO4)  have  never  been  obtained  in  a  free  state.  Several 
of  the  manganates,  however,  are  well-known  bodies.  Potassium 
manganate  (K2MnOi)  may  be  made  by  fusing  together  man- 
ganese binoxide,  caustic  potash,  and  potassium  chlorate.  The 
manganate  is  soluble  in  water,  the  ^  solution  being  of  a  green 
color.  When  this  green  solution  is  boiled  potassium  perman- 
ganate (K0Mn2O8)  is  formed,  which  gives  a  dark  purple  colored 
solution.  The  manganates  and  permanganates  readily  give  up 
oxygen  and  lose  their  color;  even  a  piece  of  wood  or  paper 
thrown  into  the  green  or  red  solution  of  a  manganate,  or  per- 
manganate, will  quickly  abstract  oxygen  from  the  solution  and 
destroy  its  color.  Potassium  permanganate  is  largely  employed 
for  disinfecting  putrid  water,  as  well  as  animal  or  vegetable 
matters  in  a  condition  of  putrefaction.  The  oxidizing  action 
of  potassium  permanganate  may  be  shown  by  the  following 
experiment. 

Exp.  210.  —  In  a  beaker  or  flask  dissolve  0.25  grm.  of  crystallized 
oxalic  acid  in  50  c.  c.  of  water,  add  5  c.  c.  strong  sulphuric  acid,  and 
warm  the  solution  to  about  60°.  Then  add  a  solution  of  potassium 
permanganate  drop  by  drop,  and  observe  that  the  color  is  at  first 
immediately  destroyed.  Continue  to  add  the  permanganate  until  it  is 
no  longer  decolorized.  The  reaction  that  has  taken  place  may  be 
thus  represented  :  — 

K2Mn208  +  5  C2H2Ot  -f  3  H2SO4  = 
2  MnS04  -f  K2S04  -+-  8  H2O  -f  10  CO2. 

The  oxalic  acid  (C2H2O4)  is  entirely  converted  into  water  and  car- 
bonic acid  :  the  potassium  permanganate  gives  up  its  oxygen  and  is 
converted  into  a  mixture  of  manganese  and  potassium  sulphates. 

On  this  property  of  potassium  permanganate  are  based  methods 
for  the  quantitative  estimation  of  readily  oxidizable  substances  such 
aa  oxalic  acid  or  the  ferrous  salts. 


264  ORES  OF  iROtfi  [§  462. 

IRON  (re). 

462.  Although  iron  is  one  of  the  most  widely  diffused  and 
most  abundant  of  the  metals,  it  is  rarely  found  native  in  the 
metallic  state.     Meteors,  however,  fall  upon  the  earth  from  outer 
space,  which  consist  mainly  of  metallic  iron,  contaminated  with 
several  other  elements  in  small  proportions.     Minerals  contain- 
ing  iron   occur  in  great  numbers ;  and  there   are  indeed  few 
natural  substances  in  which  iron  is  not  present.     It  is  found  in 
the  ashes  of  most  plants,  and  in  the  blood  of  animals.     The 
natural  compounds  of  iron  which  are  available  as  ores  of  the 
metal  are  chiefly  oxides  and  carbonates. 

From  the  richer  iron-ores  a  very  excellent  iron  can  be  ob- 
tained by  simply  heating  the  broken  ore  with  charcoal  in  an 
open  forge  fire,  urged  by  a  blast.  The  ore  is  deoxidized  by  the 
carbon  of  the  fuel,  and  the  reduced  iron  is  agglomerated  into  a 
pasty  lump  called  a  "  bloom,"  while  the  earthy  impurities  con- 
tained in  the  ore  combine  with  a  portion  of  the  oxide  of  iron  to 
form  a  fusible  glass  or  slag.  This  process  is  not  economical  in 
the  chemical  sense,  for  much  iron  is  lost  in  the  slag,  and  much 
fuel  is  burnt  to  waste  in  an  open  fire,  but  when  well  conducted 
it  yields  an  admirable  quality  of  iron,  and  is  easily  practised 
by  people  possessing  but  little  mechanical  skill  and  no  chemical 
knowledge ;  it  is  undoubtedly  the  oldest  method  of  extracting 
iron  from  its  ores. 

463.  In  the   extraction  of  iron  from  its  common  ores,  the 
metal  is  usually  obtained,  not  pure,  but  in  a  carburetted  fusi- 
ble state,  known  as  cast-iron  or  pig-iron.     The  main  features  of 
the  process  are,  first,  a  previous  calcination  or  roasting  to  expel 
water,  carbonic  acid,  sulphur  and  other  volatile  ingredients  of 
the  ore ;  secondly,  the  reduction  of  the  oxide  of  iron  to  the 
metallic  state  by  ignition  with  carbon ;  thirdly,  the  separation 
of  the  earthy  impurities  of  the  ore  by  fusion  with  other  matters 
into  a  crude  glass  or  slag;  and  lastly,  the  carbonizing  and  melt- 
ing of  the  reduced  iron.     The  preliminary  calcination  is  not 
always   essential,  but  with    many  ores,   especially  the  carbon- 
ates and  hydrates,  it  is  very  desirable ;  not  unfrequently  all  the 


§463.] 


265 


75. 


drying  necessary  is  effected  in  the  upper  part  of  the  blast-fur- 
nace itself,  within  which  the  three  last  steps  of  the  process 
always  take  place. 

The  blast-furnace  for  iron  consists  essentially  of  a  double  cone, 
built  of  fire-brick  and  masonry,  and  is  about  50  feet  in  height,  and 
from  15  to  18  feet  in  width  at  its  broadest  part.  An  idea  of  its  con- 
struction may  be  obtained  from  Fig.  75.  The  furnace  is  closed  at 
the  bottom,  the  air  necessary  for  the 
support  of  the  combustion  being  sup- 
plied by  a  powerful  blast  blown 
through  pipes  called  tuyeres  (pro- 
nounced tweers).  At  the  high  tem- 
perature produced  the  carbon  of  the 
fuel  removes  the  oxygen  from  the  iron- 
ore,  and  the  metallic  iron  is  set  free. 
The  reduction  of  the  oxide  of  iron, 
however,  is  not  alone  sufficient  to 
secure  the  metal ;  iron-ores  almost 
always  contain  earthy  admixtures, 
consisting  chiefly  of  silica,  clay  and 
calcium  carbonate,  and  these  sub- 
stances are  so  intimately  mixed  with 
the  reduced  metal,  that  it  is  essential 
to  melt  them  before  the  iron  can 
separate  by  virtue  of  its  greater  spe- 
cific gravity.  This  is  brought  about 
by  converting  these  impurities  into 
fusible  double  silicates  by  the  addition 
of  some  proper  substance  which  is 
called  a  flux.  With  ores  in  which  the  earthy  admixture  is  chiefly  cal- 
careous, the  flux  must  be  clay  or  some  siliceous  material,  but  in  the 
more  frequent  case  of  ores  containing  clay  or  silica  the  flux  will  be 
limestone  or  quicklime.  In  either  case  a  fusible  double  silicate  of 
aluminum  and  calcium  is  the  essential  constituent  of  the  slag. 

The  blast  furnace  is  charged  at  the  top  with  alternate  layers  of  the 
fuel,  (which  may  either  be  charcoal,  anthracite  or  coke)  the  ore  and 
the  flux,  which  is  generally  lime  ;  and  air  is  constantly  supplied  in 
immense  quantities  at  the  bottom  of  the  furnace.  The  blast  coming 
in  contact  with  a  great  excess  of  incandescent  carbon,  there  is 
formed  immediately  carbon  protoxide,  and  this  gas,  together  with 
23 


266  CAST-  AND   WROUGHf-IROtf.  [§  464. 

the  unaltered  nitrogen  ascends  the  shaft.  The  layers  of  solid  mate- 
rial thrown  in  at  the  top  of  the  furnace  gradually  sink  down,  and 
as  soon  as  a  stratum  of  ore  has  descended  sufficiently  to  be  heated 
by  the  hot  mixture  of  nitrogen  and  carbon  protoxide  it  becomes 
reduced  to  spongy  metallic  iron,  which,  mixed  with  the  flux  and  the 
earthy  impurities  of  the  ore,  settles  down  to  hotter  parts  of  the  fur- 
nace, where  it  enters  into  a  fusible  combination  with  carbon,  while 
the  flux  and  earthy  impurities  melt  together  to  a  liquid  slag.  The 
liquid  carburetted  iron  settles  to  the  very  bottom  of  the  furnace, 
whence  it  is  drawn  out,  at  intervals,  through  a  tapping-hole  which  is 
stopped  with  sand  when  not  in  use.  The  viscous  slag  flows  out  over 
a  dam,  so  placed  as  to  retain  the  iron,  but  to  allow  the  escape  of  the 
slag  which  floats  on  the  iron,  as  fast  as  it  accumulates  in  sufficient 
quantity.  As  fresh  portions  of  the  ore,  fuel  and  flux  are  continually 
supplied,  and  the  iron  is  withdrawn  from  time  to  time,  the  process 
goes  on  without  interruption  sometimes  for  several  years. 

The  gases  which  issue  from  the  mouth  of  the  blast-furnace  are 
charged  with  an  enormous  heating  power,  for  besides  being  them- 
selves intensely  hot  they  contain,  even  after  having  effected  the 
reduction,  a  large  proportion  of  combustible  gases,  such  as  carbon 
protoxide,  carburetted  hydrogen  and  hydrogen.  They  are,  there- 
fore, collected  at  the  top  of  the  furnace  by  a  sort  of  conical  hood,  con- 
ducted off  through  a  pipe,  and  burned  in  suitable  furnaces,  the  heat 
produced  being  utilized  in  raising  the  temperature  of  the  blast  of  air 
forced  into  the  furnace  through  the  tuyeres. 

Cast-iron  contains  from  2  to  6  per  cent  of  carbon  ;  in  white  iron, 
which  is  hard  and  brittle,  and  of  crystalline  texture,  the  carbon  seems 
to  be  mainly  in  combination  with  the  iron  ;  while  in  gray  iron,  which 
is  slightly  malleable  and  of  granular  texture,  the  carbon  exists  chiefly 
as  graphite  mechanically  disseminated  through  the  iron.  Cast-iron 
also  contains  a  small  amount  of  silicon  and  not  unfrequently  manga- 
nese ;  it  is,  moreover,  usually  contaminated  with  minute  quantities 
of  sulphur  and  phosphorus. 

464.  The  production  of  malleable  or  "wrought "-iron  from 
cast-iron  consists  essentially  in  burning  out  the  carbon,  silicon, 
sulphur  and  phosphorus  which  cast-iron  contains.  Thi?  oxida- 
tion of  the  impurities  of  cast-iron  is  effected  by  a  process  known 
as  puddling.  The  operation  consists  in  melting  the  iron  in  a 
reverberatory  furnace  and  stirring  it  so  that  the  air  will  come  in 
contact  with  it. 


466.] 


K  E  VERBERA  TOR  Y  FURNA  CE.  —  STEEL. 


267 


Fig.  76  represents  a  reverberatory  furnace,  such  as  is  used  in 
puddling.  The  principle  of  this  furnace  has  already  been  explained 
in  §  370. 

In  puddling  it  is 
customary  to  add 

to    the    charge   of  H^Wl  Fig  76. 

pig-iron  a  quantity 
of  iron  scale  or 
other  oxide  of  iron. 
The  oxidation  of 
the  silicon,  carbon, 
phosphorus,  and 
other  impurities  is 
effected  partly  by 
the  air  but  chiefly 
by  the  oxide  added  to  the  charge.  When  the  cast-iron  is  so  far 
decarbonized  as  to  be  pasty  in  the  fire,  it  is  gathered  into  lumps  on 
the  end  of  an  iron  bar  and  carried  from  the  furnace  to  a  hammer  or 
squeezer  which  expresses  the  liquid  slag  and  welds  into  a  coherent 
mass  the  tenacious  iron.  The  wrought-iron  thus  produced  has  a  gray 
color,  is  malleable  and  may  be  welded  at  a  red  heat.  It  still  con- 
tains from  0.05  to  0.25  per  cent  of  carbon. 

465.  Steel.  —  Intermediate  in  composition  between  cast-  and 
wrought-iron  as  far  as  the  amount  of  carbon  is  concerned  is 
the    invaluable    substance,  —  steel,       It    may   be    made   from 
wrought-iron  by  heating  bars  of  iron  to  redness  for  a  week 
or   more   in   contact   with   powdered    charcoal   in   close   boxes 
from  which  air  is  carefully  excluded.     Though  the  iron  is  not 
fused,    nor    the    carbon   vaporized,    yet   the    carbon    gradually 
penetrates  the  iron  and   alters   its   original   properties  ;    when 
the  bars  are  withdrawn  from  the  chests  in  which  they  were 
packed,   the  metal  has  become  fine-grained   in   fracture,  more 
brittle  and  more  fusible,  and  contains  from   1   to   2  per  cent 
of    carbon.      This    process    of    preparing    steel    is    called   the 
"  cementation "  process ;   it  is  a  curious  instance  of  chemical 
action  between  solid  materials  which  are  apparently  in  a  state  of 
rest. 

466.  A  new  and  very  rapid  method  of  preparing  cast-steel 


268  '    TKE  BESSEMER  PROCESS.  [$  467. 

directly  from  cast-iron  is  that  known  as  the  Bessemer  process. 
From  two  to  six  tons  of  cast-iron,  previously  melted  in  a  suitable 
furnace,  are  poured  into  a  large  covered  crucible,  called  the  con- 
verter, which  is  made  of  the  most  refractory  materials,  and 
swung  on  pivots  in  such  a  manner  that  it  can  be  tipped  up  and 
emptied  by  means  of  an  hydraulic  press.  Through  numerous 
apertures  in  the  bottom  of  the  crucible  a  blast  of  air  is  forced 
up  into  the  molten  metal ;  the  combustion  of  the  carbon  an^ 
silicon  of  the  iron,  as  well  as  of  a  portion  of  the  iron  itself, 
causes  an  intense  heat,  which  keeps  the  mass  fluid  in  spite  of 
its  rapid  approach  to  the  condition  of  malleable  iron.  Towards 
the  end  of  the  operation  a  sufficient  quantity  of  spiegeleisen  is 
introduced  into  the  crucible.  This  spiegeleisen  is  a  peculiar  alloy 
of  iron,  manganese  and  carbon  :  the  manganese  removes  some  of 
the  oxygen  previously  combined  with  iron  and  some  sulphur; 
the  carbon  converts  the  whole  mass  into  steel,  and  the  melted 
steel  is  immediately  cast  into  ingots. 

The  symbol  of  iron  is  Fe  (Latin,  ferrum) ;  its  atomic  weight  is  56. 

467.  Oxides  and  Hydrates  of  Iron.  —  The  best  known  of  the 
compounds  of  iron  and  oxygen  are  the  protoxide  (FeO),  or  fer- 
rous oxide,  as  it  is  often  called  ;  the  sesquioxide  (Fe2O3),  often 
called  ferric  oxide ;  and  the  magnetic  oxide  (Fe3O4). 

468.  Iron  protoxide  or  ferrous  oxide   (FeO)  may  be  ob- 
tained by  igniting  ferrous  oxalate  in  close  vessels  :   it  absorbs 
oxygen  so  rapidly  that  it  takes  fire  when  brought  in  contact 
with  the  air.     Ferrous  hydrate  (FeH2O2),  obtained  by  adding 
caustic  alkali  to  a  solution  of  a  ferrous  salt,  is  a  white  precipitate 
which  rapidly  changes  on  exposure  to  the  air  by  taking  on 
oxygen. 

469.  Iron  sesquioxide  or  ferric  oxide  (Fe2O8),  called  also 
red  oxide  of  iron,  occurs  abundantly  in  nature  as  hematite, 
specular  iron  and  red  ochre.     It  is  valuable  as  an  ore  of  iron. 
It  is  also  prepared  artificially,  and  is  much  used  as  a  pigment. 
A  fine  variety,  known  as  rouge,  is  used  for  polishing  glass  and 
jewelry.     By  heating  ferric  oxide  in  a  current  of  hydrogen,  or 
other  reducing  gas,  metallic  iron  is  readily  obtained.     This  oxide 


J  472.]  OXIDES  OF  IRON.  269 

of  iron  is  called  sesquioxide  because  it  contains  once  and  a  half 
as  many  atoms  of  oxygen  as  of  iron  (sesqui,  Latin,  one  and  a 
half). 

Ferric  hydrate  (Fe2H6O6)  may  be  prepared  by  adding  an 
excess  of  ammonia-water  to  the  solution  of  almost  any  ferric 
salt. 

Exp.  211.  —  Cover  a  teaspoonful  of  fine  iron  filings  or  small  tacks 
with  8  or  10  c.  c.  of  dilute  sulphuric  acid  in  a  small  bottle  ;  when  the 
evolution  of  hydrogen  slackens,  dilute  with  an  equal  bulk  of  water 
and  filter  into  a  small  flask.  To  the  liquid  add  a  few  drops  of 
strong  nitric  acid,  and  heat  it  to  boiling.  The  liquor  will  soon  be 
colored  dark- brown  by  the  nitrous  fumes  resulting  from  the  decom- 
position of  the  nitric  acid,  which  are  for  a  short  time  held  dissolved 
by  the  liquid  ;  but  this  deep  coloration  soon  passes  away,  and  there  is 
left  only  the  yellowish-red  color  of  the  ferric  sulphate  which  has  been 
formed.  Add  to  the  solution  ammonia- water,  until  the  odor  of  the 
latter  persists  after  agitation,  and  collect  upon  a  filter  the  flocculent 
red  precipitate  of  ferric  hydrate. 

470.  There  are  several  ferric  hydrates  which  occur  in  nature 
and  differ  somewhat  in  composition  from  this  the  normal  hy- 
drate. Yellow  ochre  is  a  variety  of  ferric  hydrate.  The  readi- 
ness with  which  ferric  oxide  gives  up  oxygen  to  reducing 
agents  is  shared  by  the  hydrate  as  well.  The  iron  nails  em- 
ployed in  the  construction  of  ships,  bridges,  fences,  or  shoes, 
actually  corrode,  "  eat  up  "  or  "  burn  out "  the  organic  matter 
in  contact  with  them,  by  absorbing  oxygen  from  the  air  and 
transferring  it  to  the  carbon  compound  with  which  they  are 
in  contact.  The  rotting  of  canvas  by  iron  rust,  or  of  a  fishing- 
line  by  the  rusty  hook,  are  familiar  instances  of  corruption  by 
rust. 

Ferric  hydrate  readily  absorbs  sulphuretted  hydrogen  with 
formation  of  an  iron  sulphide ;  it  is  much  used  on  this  account 
in  the  purification  of  coal-gas. 

.  471.  The  magnetic  oxide  of  iron  (Fe3O4)  occurs  native.  It 
is  the  richest  of  the  ores  of  iron,  and  when  pure  contains  about 
72  per  cent  of  iron. 

472.   Ferrous  and  Ferric  Salts.  —  There  are,  generally  speak 


270  FERROUS  AND  FERRIC  SALTS.  [§  473. 

ing,  two  series  of  iron  salts,  in  one  of  which  the  atom  Fe  is 
bivalent,  and  in  the  other  of  which  the  double  atom  (Fe2)  is 
sexivalent.  Thus  there  are  two  chlorides,  —  ferrous  chloride, 
FeClj,  and  ferric  chloride,  (Fe2)Cl6;  similarly  there  are  two 
nitrates,  two  sulphates,  etc. 

473.  Ferrous  Sulphate  (FeSO4).  —  A  hydrate  of  this  com- 
pound, of  composition  FeSO4  -\-  7  H2O,  usually  called  copperas 
or  green  vitriol,  is  the  most  common  of  all  the  compounds  of 
iron.     It  may  readily  be  prepared  by  dissolving  metallic  iron  or 
ferrous  sulphide  in  dilute  sulphuric  acid.     On  the  large  scale  it 
is  commonly  prepared  by  roasting  iron  pyrites  (FeS2)  at  a  gentle 
heat. 

When  perfectly  pure,  the  crystals  of  ferrous  sulphate  are 
compact,  transparent  and  of  a  bluish-green  color ;  but  in  dry 
air  they  effloresce  and  become  covered  with  a  white  incrusta- 
tion, the  color  of  which  subsequently  changes  to  rusty  brown 
through  absorption  of  oxygen.  The  common,  commercial  arti- 
cle is  of  a  grass-green  color,  and  is  contaminated  with  more 
or  less  ferric  sulphate.  When  heated,  the  crystals  first  lose 
their  water  of  crystallization,  and  on  further  application  of 
heat  the  salt  is  decomposed,  sulphurous  and  sulphuric  anhy- 
drides are  given  off,  while  ferric  oxide  remains.  Upon  this  fact 
depends  the  preparation  of  fuming  sulphuric  acid  (§  135). 

474.  Ferric  sulphate  (Fe2  3  SO4)  is  interesting,  chiefly  from 
its  analogy  with  aluminum  sulphate.     Like  the  aluminum  salt, 
it  combines  with  the  sulphates  of  the  alkali-metals,  to  form  well' 
defined  alums. 

475.  When  exposed  to  the  air,  or  to  oxidizing  agents,  the 
ferrous  salts  have  a  great  tendency  to  absorb  oxygen. 

Exp.  212.  —  Pour  a  solution  of  copperas  into  an  open  capsule, 
and  leave  it  exposed  to  the  air  for  a  day  or  two  ;  the  solution  will 
gradually  become  yellow  as  the  oxidation  proceeds,  and  after  a  while 
a  rusty  precipitate  of  ferric  oxide,  or  of  highly  basic  ferric  sulphate, 
will  fall. 

Exp.  213.  —  Dip  a  small  piece  of  cotton  cloth  in  the  solution  of 
nutgalls  prepared  in  Exp.  151,  and  allow  it  to  become  diy ;  then  dip 


§  476.]      USE  OF  FERROUS  SULPHATE  IN  DYEING.  271 

it  in  the  solution  of  copperas  and  hang  it  up  in  damp  air.  Black,  in- 
soluble iron  tannate  will  be  so  firmly  precipitated  in  and  upon  the 
fibres  of  the  cloth,  that  it  cannot  be  washed  away. 

This  experiment  illustrates  one  general  method  of  dyeing,  by  means 
of  which  blacks  and  grays  of  various  shades  may  be  applied  to  cloth 
or  leather,  though  in  practice  other  astringent  dye-stuffs,  such  as  cate- 
chu, cutch  or  gambier,  are  commonly  employed  in  place  of  nutgalls. 

Ferrous  sulphate  is  largely  employed  in  dyeing,  sometimes  directly, 
as  in  the  foregoing  experiment,  but  often  as  the  source  of  other  com- 
pounds of  iron,  which  are  employed  as  mordants  ;  ferrous  acetate,  for 
example,  obtained  by  decomposing  ferrous  sulphate  with  calcium  ace- 
tate, is  a  compound  much  used  by  dyers.  It  should  be  remarked, 
however,  that  ferrous  acetate  is  sometimes  made  directly  by  dissolv- 
ing scraps  of  iron  in  vinegar  or  pyroligneous  acid  (§  238).  Ferrous 
sulphate  is  also  used  in  dyeing  with  indigo.  Its  use  depends  upon 
the  fact,  that,  when  a  solution  of  copperas  is  treated  with  calcium  hy- 
drate, a  ferrous  hydrate  is  precipitated  ;  this  ferrous  hydrate  has  such 
a  tendency  to  absorb  oxygen,  that  a  mixture  of  copperas  and  slaked- 
lime  forms  a  powerful  reducing  mixture. 

Exp.  214.  —  Dissolve  1  grm.  of  copperas  (iron  sulphate)  in  100 
c.  c.  of  water  in  a  bottle  of  200  c.  c  capacity.  Into  the  solution  stir 
a  mixture  of  1  grm.  of  finely  powdered  indigo  and  1.5  grms.  of  freshly 
slaked  lime  ;  fill  up  the  bottle  with  water  and  cork  it.  Shake  the 
bottle  occasionally,  and,  after  eight  or  ten  hours,  pour  off,  or  remove 
with  a  pipette  (Appendix,  §  20),  a  portion  of  the  clear  and  nearly 
colorless  liquid  without  disturbing  the  precipitate  in  the  bottom  of 
the  bottle.  Expose  this  liquid  to  the  air  in  a  shallow  dish  ;  it  con- 
tains white  indigo  in  solution,  but  the  oxygen  of  the  air  rapidly  causes 
the  formation  of  blue  indigo  insoluble  in  the  liquid,  as  was  seen  in 
Exps.  159,  160,  §  342,  where  a  different  reducing  agent  was  employed. 

476.  Silicates  of  Iron.  —  Several  native  silicates  of  iron 
are  known,  but  none  of  them  are  of  special  interest.  The 
green  tinge  of  ordinary  glass  is  due  to  the  presence  of  a  fer- 
rous silicate,  and  by  increasing  the  proportion  of  the  ferrous 
salt,  a  deep  bottle-green  color  may  be  imparted  to  the  glass. 
This  color  may  be  destroyed  by  introducing  into  the  glass  dur- 
ing the  manufacture  manganese  bin  oxide,  or  some  other  ox- 
idizing agent.  The  ferrous  silicate  is  thus  converted  into 
ferric  silicate  which  has  little  coloring  power, 


272  PRUSSIAN  BLUE.  — SULPHIDES  OF  IRON.       [§  477. 

477.  Cyanides    of   Iron,  —  There    is    a    ferrous    cyanide 

(Fe(CN)2),  known  as  a  yellowish-red  precipitate,  which  takes 
up  oxygen  and  becomes  blue  when  exposed  to  the  air,  and  a 
ferric  cyanide  (Fe2(CN)6)  has  been  obtained  in  solution.  But 
by  far  the  best  known  of  the  cyanides  of  iron  are  certain 
double  compounds,  which  constitute  the  familiar  pigments, 
known,  collectively,  as  Prussian  blue.  Common  Prussian  blue 
,(Fe7C18N18  -\-  18  H2O),  may  be  regarded  as  a  compound  of  fer- 
'rous  and  ferric  cyanides,  3  Fe(CN)2,2  (Fe2(CN)6)  -}-  18  H2O;  it 
may  be  prepared  as  follows  :  — 

Exp.  215.  —  Add  to  an  exceedingly  dilute  solution  of  almost  any 
ferric  salt,  such,  for  example,  as  the  ferric  sulphate  of  Exp.  211,  a 
drop  of  potassium  ferrocyanide  (§  387).  A  beautiful  blue  precipitate 
will  form,  and  will  remain  suspended  in  the  liquor  for  a  long  while. 
Another  variety  of  Prussian  blue,  known  as  TurnbuWs  blue,  may  be 
obtained  by  mixing  a  solution  of  potassium  ferricyanide  (§  388)  with 
a  solution  of  copperas  or  other  ferrous  salt. 

Since  potassium  ferrocyanide  will  give  no  blue  coloration  with 
ferrous  salts,  and  since  the  ferricyanide  yields  no  blue  with  ferric 
salts,  it  is  evident  that  the  two  solutions  may  be  used  as  tests 
by  which  to  detect  the  presence  of  ferrous  and  ferric  salts, 
respectively,  in  any  solution. 

Exp.  216.  —  Soak  a  piece  of  cotton  cloth  in  a  solution  of  ferric 
sulphate  (Exp.  211),  and  then  immerse  it  in  an  acidulated  solution  of 
potassium  ferrocyanide.  Prussian  blue  will  be  precipitated  upon  the 
cloth,  and  will  remain  firmly  attached  to  it.  Prussian  blue  is  largely 
employed  in  dyeing  and  calico  printing  in  a  variety  of  ways. 

478.  Iron  protosulphide  (FeS)  is  a  substance  of  great  value 
to  the  chemist  as  the  cheapest  source  of  the  important  reagent, 
sulphuretted   hydrogen   (§  121).     The   sulphide  may  be  pre- 
pared by  igniting   pyrites  in   a   covered   crucible,    by   rubbing 
roll   brimstone  against  a  white  hot  iron  bar,  or   by  fusing  to- 
gether sulphur  and  iron  turnings  (Exp.  47,  §  115). 

Exp.  217.  —  Dissolve  a  small  crystal  of  ferrous  sulphate  (cop- 
peras) in  water,  and  add  to  the  liquid  a  drop  or  two  of  ammonium 
sulphydrate  (  §  401).  Black  iron  sulphide  will  be  thrown  down. 
The  finely  divided  protosulphide  thus  obtained  in  the  wet  way,  dis- 


J  481.]  COBALT  AND  NICKEL.  273 

solves  much,  more  quickly  in  acids  than  the  compact  sulphide  obtained 
by  the  way  of  fusion  ;  in  contact  with  acids  it  evolves  gas  so  turnultu- 
ously  that  it  would  be  inconvenient  as  a  source  of  hydrogen  sulphide. 
The  black  earth  between  the  stones  of  the  pavements  of  cities,  and 
at  the  bottom  of  drains  and  cesspools,  owes  its  color  to  iron  proto- 
sulphide  formed  by  the  putrefaction  of  sulphuretted  compounds  in 
contact  with  ferric  oxide  contained  in  the  earth. 

479.  Iron  bisulphide  (FeS2)  occurs  abundantly  in  nature  as  the 
well-known  mineral  iron  pyrites.     When  the  pyrites  is  roasted 
at   a  high  temperature,    sulphurous  anhydride   is  formed,   and 
ferric    oxide    left,    as   in   the   manufacture   of    sulphuric   acid. 
When  the  temperature  of  the  burning  pyrites  is  kept  low,  the 
product  is  principally  ferrous  sulphate,  and  a  large  amount  of 
copperas  is  thus  obtained  by  roasting  pyrites  and  then  treating 
with  water.     Under  certain  conditions  pyrites  oxidizes  in  the  air 
at  the  ordinary  temperature ;  the  spontaneous  combustion  of 
many  kinds  of  coal  is  due  to  the  oxidation  of  iron  pyrites  dis- 
seminated through  the  combustible. 

COBALT    (CO)    AND    NICKEL    (Nl). 

480.  Cobalt  and  nickel  are  two  metals  remarkably  similar  to 
each   other  in  both  physical  and  chemical  properties.     They  occur 
together  in  nature,  generally  in  combination  with  sulphur  and  arsenic. 
They  have  the  same  atomic  weight  (58.8)  and  nearly  the  same  specific 
gravity  (8.2  to  8.9).     Nickel  is  somewhat  used  as  an  ingredient  of 
certain  alloys,  of  which  German  silver,  composed  of  copper,  zinc  and 
nickel,  is  the  most  familiar. 

Like  iron,  cobalt  and  nickel  form  protoxides  (CoO  and  NiO)  and 
corresponding  proto-salts  ;  like  iron,  they  form  sesquioxides  (Co2O3 
and  Ni2O3)  and  corresponding  per-salts.  Unlike  iron,  however,  the 
protoxides  are  more  stable  compounds  than  the  sesquioxides.  To 
designate  the  two  series  of  salts,  the  terms  cobaltous  and  cobaltic, 
nickelous  and  nickelic  are  sometimes  employed. 

481.  The   Sesquioxide   Group.  —  The  most   striking  char- 
acteristic of  the  metals  which  have  been  grouped  together   in 
this   chapter   is   the   property  which   they  possess  of  forming 
sesquioxides  and  a  corresponding  series  of  salts ;  most  of  them 


274  COPPER.  [§  482. 

form  protoxides  as  well,  and  if  we  arrange  the  metals  in  the 
order  of  their  atomic  weights, 

Gl  =  14,  Al  =  27.4,  Cr  =  52.5,  Mn  =  55,  Fe  =  56, 
Ni  =  58.8,  Co  =  58.8, 

the  sesquioxides  of  the  metals  at  the  head  of  the  list  are  the 
most  stable  of  the  sesquioxides,  and  the  protoxides  of  nickel 
and  cobalt  are  the  most  stable  of  the  protoxides,  while  with 
manganese  and  iron  both  forms  of  oxide  are  well  represented. 
Glucinum  and  aluminum  have  no  protoxides  at  all,  and  the 
protoxide  of  chromium  is  very  unstable. 

482.  Uranium  (Ur)  (at.  wt.  =  120).  — With  the  members  of  this 
group  may  be  classed  the  rare  metal  uranium,  the  sesquioxide  of 
which  is  used  to  give  a  beautiful  yellowish-green  color  to  glass,  and  also 
the  following  elements,  which  are  more  or  less  nearly  related  to  alumi- 
num and  iron  : — Yttrium,  Yt;  Erbium,  Er;  Zirconium,  Zr;  Cerium, 
Ce ;  Lanthanum,  La ;  Didymium,  Di ;  Thorium,  Th ;  Gallium,  Ga. 


CHAPTER  XXVII. 
COPPEE  AND  MERCURY. 

COPPER    (CU). 

483.  Though  by  no  means  one  of  the  most  abundant  metals, 
copper  is  nevertheless  very  widely  diffused  in  nature,  and  is 
largely  employed  by  man.  Traces  of  it  exist  in  almost  every 
soil,  whence  it  is  taken  up  by  plants,  in  which  it  may  almost 
always  be  detected  by  refined  testing.  Traces  of  it  have 
repeatedly  been  found  also  in  the  various  animal  organs  and 
secretions.  Besides  occurring  in  the  native  state,  copper  is 
found  in  a  great  variety  of  combinations ;  the  most  common  of 
its  ores,  however,  is  the  sulphide,  or  rather  a  compound  of  cop- 
per sulphide  and  iron  sulphide  in  varying  proportions,  known  as 
copper  pyrites.  The  carbonates  and  oxides  of  copper  are  also 
valuable  as  ores. 


§  487.]         COMPOUNDS  AND  ALLOYS  OF  COPPER.  275 

484.  Copper  is  a  rather   hard    metal,  of  a  well-known   red 
color ;  it  is  very  tenacious,  ductile  and  malleable.     At  the  or- 
dinary  temperature   the    metal  is  not  altered  in  dry  or  moist 
air,  unless  finely  divided.     When  heated  in  the  air  it  becomes 
covered  with  a   coating  of  a  black  oxide.     Metallic  copper  is 
not  very  readily  acted  upon  by  acids,  excepting  those  rich  in 
oxygen.     Except  when  finely  divided  it  is  scarcely  acted  upon 
by  even  concentrated  chlorhydric  acid ;  in  hot  sulphuric  acid  it 
dissolves  as  copper  sulphate,  sulphurous  anhydride  being  given 
off;   in  nitric   acid   somewhat   diluted,   it   dissolves   readily  as 
copper  nitrate,  and  nitric  oxide  escapes  (Exp.  19,  §  50). 

485.  Several  of  the  compounds  of  copper  with  other  metals 
are  of  great  importance  in  the  arts.      Brass  and  the   yellow- 
metal  used  for  sheathing  ships  are  alloys  of  zinc  and  copper; 
bronze,  gun-metal  and  bell-metal  are  alloys  of  tin  and  copper, 
and  various  compositions  are   produced  by  mixing  these  alloys 
with  brass  ;  copper  is  also  an  essential  ingredient  of  all  the 
common  coins,  implements  and  ornaments  of  gold  and  silver. 

486.  Cuprous  and  Cupric  Salts.  —  There  are  two  series  of 
copper  salts,  in  one  of  which  the  atom  Cu  is  bivalent,  while 
in  the  other  the  double  atom  Cu2  is  bivalent.     Thus,  cupric 
chloride  is  CuCl2 ;  cuprous  chloride  is  Cu2Cl2.     As  a  rule  the 
cupric  salts  are  the  more  common  and  the  more  stable  of  the 
two  series. 

487.  Oxides  of  Copper.  —  There  are  two  oxides  of  copper. 
Copper  suboxide,  cuprous  oxide  or  red  oxide  of  copper  (Cu2o) 
occurs  in  nature  as  "  ruby  copper."     It  may  be  prepared  artifi- 
cially in  various  ways,  as,  for  example,  by  the  action  of  certain 
reducing  agents  on  alkaline  solutions  of  cupric  salts  (Exp.  135, 
§  298).     Cuprous  oxide  is  used  to  give  a  ruby-red  color  to  glass. 
Copper  oxide,  cupric  oxide  or  black  oxide  of  copper  (CuO) 
may  be  prepared  by  heating  the  metal  in  a  current  of  air,  or  by 
igniting  the  carbonate,  hydrate  or  nitrate. 

Exp.  218.  —  Bind  a  bright  copper  coin  with  wire,  in  such  man- 
ner that  a  strip  of  wire  8  or  10  c.  m.  long  shall  be  left  projecting  from 
the  coin  ;  thrust  the  free  end  of  the  wire  into  a  long  cork  or  bit  of 


276  COPPER  HYDRATE.  [§  488. 

wood,  and  by  means  of  this  handle  hold  the  coin  obliquely  in  a  small 
flame  of  the  gas-lamp.  A  beautiful  play  of  iridescent  colors  will  ap- 
pear upon  the  surface  of  the  copper,  particularly  if  it  be  moved  to 
and  fro.  Thrust  the  hot  coin  into  water,  and  observe  that  it  is  at 
this  stage  covered  with  a  red  coating  of  copper  suboxide.  Replace 
the  coin  in  the  lamp  and  hold  it  in  the  hot  oxidizing  portion  of  the 
flame  ;  it  will  soon  become  black  from  the  formation  of  copper  prot- 
oxide. After  a  rather  thick  coating  of  oxide  has  been  formed,  again 
quench  the  coin  in  water  :  the  black  coating  or  scale  of  oxide  will  fall 
off,  and  beneath  it  will  be  seen  a  thin  film  of  the  suboxide  firmly  ad- 
hering to  the  metal. 

Exp.  219.  —  Evaporate  to  dryness  in  a  porcelain  dish  upon  a 
sand-bath  some  of  a  solution  of  copper  nitrate  prepared  from  copper, 
as  in  Exp.  21.  Place  a  small  quantity  of  the  dry  residue  upon  a 
fragment  of  porcelain,  and  ignite  it  until  red  nitrous  fumes  are  no 
longer  given  off.  Copper  protoxide  will  be  left  upon  the  porcelain. 

488.  Copper  hydrate  (CuH2O2)  is  formed  when  caustic  alkali 
is  added  to  a  solution  of  a  salt  of  copper. 

Exp.  220.  —  Place  in  a  test-tube,  or  small  bottle,  8  or  10  c.  c.  of 
a  cold  dilute  solution  of  copper  sulphate,  and  add  to  it  enough  of  a 
solution  of  caustic  soda  to  render  the  mixture  alkaline  to  test-paper. 
A  light  blue  precipitate  will  fall ;  hydrate  of  copper  is  insoluble  in 
water  and  in  soda  lye. 

Exp.  221.  —  Repeat  Exp.  220,  with  the  difference  that  the  solu- 
tions of  caustic  soda  and  copper  sulphate  are  both  heated  to  boiling, 
and  are  mixed  while  hot.  Instead  of  the  blue  hydrate,  black  copper 
protoxide  will  now  be  thrown  down,  for  copper  hydrate  readily  parts 
with  its  water  when  heated,  even  if  it  be  all  the  while  immersed  in 
water  ;  it  does  not  again  combine  with  water  after  it  has  become 
cold. 

Exp.  222.  — Again  repeat  Exp.  220,  but  instead  of  soda  lye  add 
to  the  copper  salt  ammonia- water,  drop  by  drop,  and  shake  the  tube 
after  each  addition  of  the  ammonia.  Copper  hydrate  will  be  precipi- 
tated as  before  in  accordance  with  the  reaction, 

CuS04  -f  2  (NH4)HO  =  (NH4)2S04  -f  CuH2O2, 

for,  as  has  been  said,  this  hydrate  is  insoluble  in  water  ;  but  since 
copper  hydrate  is  readily  soluble  in  ammonia-water,  the  precipitate 
will  redissolve  as  soon  as  more  of  this  agent  than  is  needed  to  decom- 
pose the  copper  salt  is  added.  The  ammoniacal  solution  of  copper 
has  a  magnificent  azure-blue  color. 


§  491.]  EXTRACTION  OF  MERCURY.  277 

489.  Copper  sulphate  (CuSO4)  may  be  obtained  by  treating 
metallic  copper  with  hot  sulphuric  acid  (see  §  123),  or  by  dis- 
solving copper   oxide  in  dilute  sulphuric  acid.     The  salt  crys- 
tallizes  with    5    equivalents  of   water.      This  hydrated  salt  is 
known  as  blue  vitriol,  and  is  much  used  in  the  arts. 

It  is  remarkable  that  the  blue  color  of  copper  sulphate  de- 
pends upon  the  presence  of  water. 

Exp.  223.  —  Heat  a  little  powdered  blue  copper  sulphate  upon 
a  piece  of  porcelain  ;  as  it  loses  its  water,  the  light-blue  powder  will 
turn  white.  A  drop  of  water  upon  the  anhydrous  powder  will  restore 
the  blue  color. 

490.  Acetates  of  copper  are  formed  by  the  action  of  acetic 
acid  upon  metallic  copper  exposed  to  the  air.     They  are  com- 
monly  called   verdigris.      Verdigris    is   usually   prepared    by 
packing   plates    of  copper   between  woollen   cloths  steeped   in 
vinegar.     The  term  is  often,  although  incorrectly,  applied  to  the 
green  coating  of  carbonate  which  forms  on  metallic  copper  when 
long  exposed  to  moist  air. 

Sulphides  of  copper  (Cu2S  and  CuS)  occur  native,  and  the 
double  sulphide  of  copper  and  iron  called  copper  pyrites  has 
already  been  mentioned  as  an  ore  of  copper.  Cupric  sulphide 
(CuS)  is  of  considerable  importance  to  the  analyst ;  it  is  formed 
when  hydrogen  sulphide  is  passed  into  a  solution  of  a  cupric  salt, 
and  is  a  black  powder,  insoluble  in  water,  in  dilute  acids,  and  in 
alkaline  solutions. 

MERCURY   (Hg). 

491.  Small  globules  of  metallic  mercury  are  sometimes  found 
in    nature ;    but    the   principal    ore   of  this  metal   is    the    sul- 
phide HgS,  called  cinnabar.     From  this  sulphide  the  metal  is 
readily  extracted  by  distilling  a  mixture  of  it  and  quicklime,  or 
iron-turnings,  in  cast-iron  retorts.     The  sulphur  is  retained  by 
the  lime,  or  iron,  as  the  case  may  be,  while  metallic  mercury 
passes  off  in  the  state  of  vapor  into  receivers  containing  water, 
beneath  which  it  condenses  to  the  liquid  state.     Large  quan- 
tities of  mercury  are  used  in  extracting  gold  and  silver  from 


278  COMPOUNDS  OF  MERCURY.  [§492. 

their  ores,  for  silvering  mirrors,  and  in  the  process  of  fire- 
gilding.  Preparations  of  mercury  are  employed  also  as  medica- 
ments, and  for  various  purposes  in  the  useful  arts.  The  fluidity 
of  the  metal  makes  it  valuable  in  the  construction  of  certain 
philosophical  instruments,  of  which  the  thermometer  and  barom- 
eter are  familiar  examples. 

492.  At  the  ordinary  temperature  of  the  air  mercury  is  a 
brilliant,  mobile  liquid,  of  13.6  specific  gravity;  it  freezes  at 

—  39.4°,  becoming  a  ductile  solid  of  tin- white  color  and  granu- 
lar fracture,  which  can  be  cut  with  a  knife.  Mercury  vaporizes 
slowly,  even  at  ordinary  temperatures,  and  boils  at  about  360°. 
The  specific  gravity  of  mercury  vapor  is  100,  its  atomic  weight 
200.  The  symbol  Hg  thus  denotes  the  two-volume  weight  of 
this  element  (§  140),  and  the  molecule  of  mercury  is  regarded  as 
containing  but  a  single  atom. 

493.  Pure  mercury  is  unacted  upon  by  the  air  at  the  ordi- 
nary temperature ;  when  heated  it  is  converted  into  the  red 
oxide.     It  is  not  attacked  by  chlorhydric  acid  ;  hot   sulphuric 
acid  converts  it  into  mercury  sulphate ;  it  dissolves  readily  in 
nitric  acid. 

494.  Compounds   of  Mercury.  —  There  are  two   oxides  of 
mercury,  —  an  unstable  black  suboxide  (Hg2O)  and  the  ordinary 
red  mercury  oxide  (HgO).     This  latter  oxide,  as  commonly  pre- 
pared  by  heating  mercury  in  the  air,  or  by  gently  heating  mer- 
cury nitrate,  is  a  compact,  granular,  almost  crystalline,  glisten- 
ing powder,  of  bright  brick-red  color ;  but  when  prepared  in  the 
wet  way  by  adding  caustic  alkali  to  a  solution  of  a  mercuric  salt, 
it  is,  when  dry,  a  soft,  orange-colored  powder.     Mercury  oxide 
is  decomposed  by  heat,  as  has  already  been  seen  (Exp.  3,  §  9). 
Corresponding  to  the  oxides  of  mercury  are  two  series  of  com- 
pounds, the  mercuric  salts  in  which  the  atom  Hg  is  bivalent, 
and   the   mercurous   salts   in   which   the  double  atom  Hg,,  is 
bivalent. 

495.  Mercuric  sulphide  (HgS),  which  occurs  native  as  cin- 
nabar, is  the  most  important  ore  of  mercury.     An  artificial  pro- 
duct of  the  same  composition,  known  as  vermilion,  is  used  as  a 


§  498.]  AMALGAMS.  279 

pigment.  The  same  compound  is  formed  when  hydrogen  sul- 
phide is  passed  into  a  solution  of  a  mercuric  salt ;  thus  prepared 
it  is  of  a  black  color.  It  is  insoluble  in  water,  in  dilute  acids, 
and  nearly  insoluble  in  alkaline  liquids. 

496.  Mercurous  chloride  (Hg2Cl2),  commonly  called  calomel, 
is  extensively  used    as    a    medicament.     It   is    a   heavy  white 
powder,  which  volatilizes  at  temperatures   below  redness  with- 
out  previous   fusion.     It  is  tasteless,  odorless,  and  as  good  as 
insoluble  in  water. 

497.  Mercuric  chloride  (HgCl2),  better  known  by  the  name 
of  corrosive  sublimate,  commonly  occurs  in  commerce,  in  trans- 
lucent, crystalline  masses.     It  melts  at  about  265°,  forming  a 
colorless  liquid,  which  boils  at  293°  ;  the  fumes  are  acrid,  and, 
like  the  salt  itself,  exceedingly  poisonous. 

Mercuric  chloride  unites  with  many  organic  substances  to 
form  compounds  insoluble  in  water  and  imputrescible.  It  co- 
agulates albumin,  for  example,  and  the  more  perishable  portions 
of  wood ;  hence  the  employment  of  raw  white  of  egg  as  an 
antidote  in  cases  of  poisoning  by  corrosive  sublimate,  and 
the  use  of  the  mercury  salt  for  preserving  wood,  —  a  purpose 
for  which  it  would,  no  doubt,  be  largely  employed  were  it 
not  for  its  high  cost.  Collections  of  dried  plants,  and  of  other 
objects  of  natural  history,  are  preserved  both  from  decay  and 
from  the  attacks  of  insects  by  brushing  over  them  a  solution 
of  the  chloride  in  alcohol. 

498.  Amalgams.  —  Mercury  unites  with  most  of  the  other 
metals  to  form  alloys,  many  of  which  are  pasty,  or  even  liquid, 
when  the    proportion  of  mercury   contained  in  them  is  large. 
These    alloys    are   commonly   called    amalgams,    in   contradis- 
tinction  to  the  ordinary  solid  alloys  of  the  other  metals,   in 
which  mercury   has  no  place.     The  liquid  amalgams  are  true 
solutions  of  other   metals,  or  of  solid  amalgams,   in  the  fluid 
mercury.     The   so-called   silvering   of   mirrors   is   an   amalgam 
of  tin. 

Mercury  may  be  detected  in  almost  any  soluble  salt  of  the 
element  by  introducing  into  a  solution  of  the  salt  a  piece  of 
clean  copper. 


280  CRYSTALLIZATION  OF  TIK  [§  499. 

Exp.  224.  —  Place  a  drop  of  a  solution  of  either  of  the  nitrates  or 
chlorides  of  mercury  upon  a  copper  coin  and  rub  the  liquid  over  its 
surface.  A  white  coating  of  metallic  mercury  will  be  deposited  upon 
the  metal. 


CHAPTER  XXVIII. 

TIN  (Sn). 

499.  Though  by  no  means  widely  diffused  in  nature,  and 
though  ores  of  it  occur  in  but  few  localities,  tin  is  one  of  the 
metals  which  have  longest  been  known  to  man.  The  principal 
ore  of  tin  is  the  binoxide,  called  tin-stone.  In  order  to  extract 
the  metal  from  it,  the  tin-stone  is  mixed  with  powdered  coal, 
and  heated  upon  the  hearth  of  a  reverberatory  furnace  in  a 
reducing  flame.  The  reduced  metal  melts  readily,  and  is  then 
run  out  of  the  furnace  into  iron  moulds. 

Tin  is  a  lustrous  white  metal,  soft,  malleable  and  ductile, 
though  not  very  tenacious.  Its  ductility  varies  greatly  with 
the  temperature;  at  100°  the  metal  may  be  drawn  into  thin 
wire,  but  at  200°  it  is  very  brittle.  When  a  bar  of  tin  is  bent 
it  emits  a  peculiar  crackling  sound,  and  if  the  bending  be 
repeated  the  metal  becomes  decidedly  warm.  These  phenomena 
appear  to  depend  on  the  disturbance  of  interlaced  crystals  con- 
tained in  the  bar,  and  upon  the  friction  of  these  crystals  one 
against  the  other.  Tin  always  exhibits  a  great  tendency  to 
assume  the  crystalline  form,  in  passing  from  the  liquid  to  the 
solid  condition.  Upon  this  peculiarity  is  founded  a  method  of 
ornamenting  tinned  iron. 

Exp.  225.  —  Heat  a  piece  of  common  tinned  iron  over  the  gas 
lamp  until  the  tin  has  melted,  thrust  the  plate  into  cold  water  in  order 
that  the  tin  may  harden  quickly,  then  remove  the  smooth  surface  of 
the  metal  by  rubbing  it  first  with  a  bit  of  paper  moistened  with  dilute 
aqua  regia,  and  then  with  paper  wet  with  soda-lye.  By  this  treat- 
ment there  will  soon  be  laid  bare  a  new  surface  covered  with  beautiful 
crystalline  figures,  like  frost  upon  a  window-pane. 


§  503.]  GOLD.  281 

500.  Tin  does  not  tarnish  in  the  air  at  ordinary  temperatures, 
and  for  this  reason,  as  well  as  on  account  of  its  brilliant  lustre, 
tin  is  largely  employed  for  coating  other  metals,  —  copper,  for 
example,  as  in  ordinary  pins,  cooking  vessels  and  bath-tubs,  — 
and  iron,  as  in  common  sheet-tin,  of  which  the  so-called  tin- 
ware is  manufactured. 

501.  The  alloys  of  tin  are  important.     The  composition  of 
bronze,    bell-metal,    etc.,    has    been    already   mentioned    under 
copper  (§  485),  and  that  of  stereotype  metal  under  antimony 
(§  165).     Of  the  other  alloys  of  tin  those  formed  by  its  union 
with  lead  are  most  remarkable.     Plumbers'  solder  consists  com- 
monly of  equal  parts  of  lead  and  tin,  though  some  kinds  of 
it  contain  only  one-third  their  weight  of  lead,  and  others  only 
one-third   their   weight   of  tin.      Pewter   is    composed   of   tin, 
together  with  a  small  proportion  of  lead,  and  sometimes  anti- 
mony. 

502.  Compounds  of  Tin.  —  There  are  two  oxides  of  tin,  — 
tin  protoxide  (SnO)  and  tin  binoxide  (SnO2).     The  latter  oc- 
curs native,  and  is  the  principal  ore  of  tin,  as  already  stated. 
The  binoxide   may  be  prepared   in  the  hydrated  form,  and  is 
known  as  stannic  acid.      Sodium  stannate  is  used  in  dyeing. 
Tin  bisulphide  (SnS2)  is  a  bright  golden-yellow  powder  known 
as  mosaic  gold,  and  used  in  decorative  painting.     The  chlorides 
of  tin  (SnCl2  and  SnCl4)  are  the  most  important  of  the  com- 
pounds of  tin,  and  are  much  used  in  dyeing. 


CHAPTER  XXIX. 
GOLD  AND  PLATINUM, 

GOLD  (AU). 

503.  Though  generally  found  only  in  small  quantities,  gold 
is  very  widely  diffused  upon  the  surface  of  the  globe.  Traces 
of  it  may  be  found  beneath  the  sandy  beds  of  most  rivers,  and  it 
occurs  iii  many  of  the  crystalline  rocks  and  in  the  soils  result- 


282  ALLOYS  OF  GOLD.  [§  504. 

ing  from  their  decomposition.  Many  varieties  of  iron  pyrites 
in  particular  contain  appreciable  quantities  of  gold,  and  silver 
is  never  found  in  nature  altogether  free  from  it.  The  chief 
source  of  the  metal  as  an  article  of  commerce  is  native  gold ; 
this  is  sometimes  found  in  a  condition  of  purity,  but  is  usually 
alloyed  with  more  or  less  silver.  It  is  collected,  either  directly 
by  mechanically  washing  away  the  lighter  substances  with 
which  it  is  associated,  or,  in  the  case  of  poorer  ores,  the  gold 
is  dissolved  out  chemically  by  means  of  quicksilver,  and  is  sub- 
sequently recovered  from  the  amalgam  by  nitration  and  dis- 
tillation. 

504.  Pure  gold  is  remarkable  as  being  the  most  malleable  of 
the  metals.     Its  softness  is  nearly  as  great  as  that  of  lead.     It 
has,  however,  much  tenacity,  and  may  be  drawn  into  extremely 
fine  wire;    1    grm.   of  gold    can   be   made   to   yield   as   much 
as  3  kilometres  of  wire.     The  metal  can  be  beaten  into  leaves 
which    are    not  more  than  T^^  of  a  millimetre  thick,     The 
specific   gravity  of  gold  is   about    19.3;   its   atomic  weight   is 
196. 

505.  In  the  air,  gold  undergoes  no  change  at  temperatures 
lower  than  its  melting-point ;  and  upon  this  fact,  taken  in  con- 
nection with  the  beautiful  color  and  lustre  of  the  metal,  and  its 
comparative  rarity,  its  principal  uses  depend. 

On  account  of  this  indestructibility,  gold  was  regarded  by 
the  earlier  chemists  as  the  king  of  metals ;  together  with  plati- 
num and  silver  it  is  still  spoken  of  as  a  noble  metal,  Few 
chemical  agents,  excepting  melted  metals,  have  any  action  upon 
gold.  None  of  the  common  acids,  when  taken  singly,  can 
dissolve  it,  though  the  metal  is  completely  soluble  in  a  mix- 
ture of  chlorhydric  and  nitric  acids  (§  75),  and  is  not  completely 
insoluble  in  nitric  acid  contaminated  with  nitrous  acid  or  with 
nitrogen  peroxide.  The  elements  chlorine  and  bromine,  how- 
ever, unite  with  it  in  the  cold,  and  when  hot  it  is  attacked  by 
phosphorus  and  arsenic. 

506.  Alloys  of  Gold.  —  Gold  unites  with  most  of  the  other 
metals  ;   but  its  most  important  alloys   are  those  with  copper, 
silver,  and  mercury.     Pure  gold  is  so  soft  that  articles  of  jew- 


«  509  !  PROPERTIES  OF  PLATINUM.  283 

o  *  J 

elry  made  of  it  would  quickly  wear  out  if  used ;  such  articles, 
as  well  as  coins  and  watches,  are"  therefore  always  made  of  gold 
which  has  been  alloyed  with  copper,  in  order  to  increase 
its  hardness.  The  standard  alloy  for  coin  in  this  country 
and  in  France  is  nine  parts  by  weight  of  gold  to  one  part 
of  copper ;  in  England  it  is  eleven  parts  of  gold  to  one  of 
copper. 

507.  Salts  of  Gold,  —  The   compounds   of  gold   have   little 
chemical  interest ;   two  oxides  are  known  (Au2O  and  Au2O3) ; 
the  chloride  (AuCl3)  is  somewhat  used  in  the  chemical  labor- 
atory ;  and  the  cyanide  or  rather  a  solution  of  gold  cyanide  in 
potassium  cyanide  is  used  in  electro-gilding. 

PLATINUM  (pt). 

508.  Platinum  is  a  metal  which,  like  gold,  has  little  affinity 
for  the  other  chemical  elements.     It  is  commonly  found  in  the 
native  state,  alloyed  with  gold  and  with  other  metals.     Like 
gold,  it  is  obtained  by  washing  away  the  earth  and  sand  with 
which  it  is  found  mixed.     It  is  a  very  heavy  metal,  the  specific 
gravity  of   cast-platinum   being  21.15.     Its   atomic   weight   is 
197.4.     The    color   of   platinum   is   intermediate   between   the 
white  of  silver  and  the  gray  of  steel ;  its  lustre  is  far  less  bril- 
liant than  that  of  silver.     It  is  as  soft  as  copper,  very  mallea- 
ble and  very  tenacious ;  it  may  be  drawn  into  wire  so  fine  that 
its  diameter  is  only  y^o  of  a  millimetre.     It  is  not  fusible  in 
ordinary  furnaces,  but  may  be  used  in  the  blowpipe  flame,  and 
is  nowadays  melted  in  considerable  quantities  in  lime  crucibles 
by  means  of  a  blowpipe  flame  obtained  from  common  coal-gas 
and  oxygen. 

509.  Platinum  does  not  oxidize  in  the  air  at  any  temperature, 
nor  is  it  attacked  by  any  of  the  common  acids  taken  separately ; 
in  aqua  regia  (§  75)  it  dissolves  slowly,  —  much  less  readily 
than  gold.     Chlorine- water  dissolves  it,  but  neither  bromine  nor 
iodine  has  any  action  upon  it. 

From  its  comparative  inertness  as  a  chemical  agent,  taken  in 
connection  with  its  infusibility,  platinum  is  an  extremely  useful 
metal  to  the  chemist.  It  is  employed  in  the  scientific  laboratory 


284  PLATINUM  BLACK.  [§510. 

for  crucibles,  evaporating  dishes,  stills,  tubes,  spatula,  forceps, 
wire,  blowpipe  tips,  and  the  like ;  and  in  the  manufacture  of  oil 
of  vitriol,  large  platinum  stills,  together  with  cooling  siphons  of 
the  same  metal,  are  employed  in  the  process  of  concentrating  the 
acid. 

With  most  of  the  other  metals  platinum  unites  readily,  form- 
ing alloys  which  in  many  instances  are  more  fusible  than  pla- 
tinum itself ;  hence,  in  employing  platinum  vessels  in  chemical 
experiments,  care  mus$  be  taken  never  to  touch  the  platinum 
with  easily  fusible  metals,  or  to  place  in  the  vessels  any  easily 
reducible  compound  of  a  metal. 

510.  A  remarkable  property  of  platinum  is  that  of  inducing 
various  gases  to  combine  chejnically  one  with  the  other.  This 
power  of  causing  combination  is  possessed  even  by  clean  sur- 
faces of  the  ordinary  solid  metal,  though  to  a  much  greater 
degree  by  spongy  platinum  (Exp.  228),  and  still  more  by  the 
very  finely  divided  powder  known  as  platinum  black. 

Exp.  226.  —  Cut  half  a  gramme,  or  more,  of  worn-out  platinum 
foil,  or  wire,  into  small  fragments,  and  boil  them  with  a  teaspoonful  of 
aqua  regia  so  long  as  the  metal  appears  to  be  acted  upon,  then  decant 
the  liquid  into  a  porcelain  dish,  add  to  the  fragments  of  platinum 
another  teaspoonful  of  aqua  regia,  and  proceed  as  before,  repeating 
the  treatment  until  all  the  metal  has  dissolved.  By  the  repeated 
action  of  successive  small  portions  of  the  solvent,  platinum  and  other 
comparatively  insoluble  substances  can  be  dissolved  much  more  read- 
ily than  if  all  the  liquid  necessary  for  its  solution  were  added  at  once. 
Evaporate  the  solution  to  dryness  upon  a  water-bath,  take  up  the 
residue  with  water,  and  preserve  the  solution  of  platinum  chloride 
(PtCl4)  thus  obtained  in  a  bottle  provided  with  a  glass  stopper. 

Exp.  227. —  Pour  a  teaspoonful  of  a  solution  of  ammonium  chlo- 
ride into  a  test-tube,  acidulate  the  liquid  with  chlorhydric  acid, 
and  add  to  it  a  drop  of  the  solution  of  the  platinum  chloride  obtained 
in  the  preceding  experiment.  A  yellow,  insoluble  powder  will  soon  be 
precipitated.  The  composition  of  this  precipitate  moy  be  represented 
by  the  formula  2  NH4C1,  PtCl4.  Repeat  the  experiment,  and  this 
time  take  enough  of  the  platinum  solution  and  of  the  ammonium 
chloride  to  make  half  a  teaspoonful  of  the  yellow  precipitate,  taking 
care  that  at  last  there  shall  be  a  slight  excess  of  free  ammonium 
chloride  rather  than  of  platinum  chloride  in  the  supernatant  liquid. 
Allow  the  precipitate  to  settle,  separate  it  from  the  clear  liquor  by 


§  512.]  THE  PLATINUM  GROUP.  285 

decantation,  and  dry  it  partially  at  a  gentle  heat.  When  the  precipi- 
tate has  acquired  the  consistence  of  slightly  moistened  earth,  trans- 
fer it  to  a  cup-shaped  piece  of  platinum  foil,  and  heat  it  to  redness  in 
the  gas  flame,  as  long  as  fumes  of  ammonium  chloride  continue  to 
escape.  All  the  chlorine,  hydrogen,  and  nitrogen  will  he  driven  off", 
and  there  will  remain  upon  the  foil  a  gray,  loosely-coherent,  sponge- 
like  mass  of  metallic  platinum  ;  it  is  called  platinum  sponge. 

Exp.  228.  — Hold  the  dry  platinum  sponge  of  Exp.  227  in  a 
stream  of  hydrogen  or  of  common  illuminating  gas  issuing  from  a 
fine  jet.  The  metal  will  soon  hegin  to  glow,  and  in  a  moment  will 
become  hot  enough  to  inflame  the  mixture  of  air  and  gas  in  contact 
with  it.  Before  friction-matches  were  employed,  this  property  of 
spongy  platinum,  of  inflaming  hydrogen,  was  sometimes  made  use 
of  for  striking  a  light.  The  mode  of  action  of  the  platinum  in  this 
experiment  is  obscure  ;  it  has  already  been  alluded  to  in  §  127. 

511.  Platinum  black  is  a  term  applied  to  metallic  platinum, 
even   more    finely   divided   than   the   sponge   above   described. 
Platinum  black  is  not  only  capable  of  absorbing   and  storing 
up  many  times  its  own  bulk  of  oxygen  gas,  but  it  is  also  capa- 
ble of  giving  away  this  oxygen  to  many  other  substances.     If 
easily  oxidizable  liquids,  such  as  alcohol  or  ether,  are  dropped 
upon  platinum  black  which  has  previously  been  exposed  to  the 
air,  the  liquids  will  be  oxidized   and  converted  into  new  sub- 
stances, while  the  powder  becomes  red-hot  from  the  heat  evolved 
during  the  act  of  oxidation. 

512.  With  gold  and  platinum  are  classed  several  rare  metals,  which 
are  never  found  except  in  association  with  platinum,  and  which  closely 
resemble  that  metal.     They  are  commonly  called  platinum  metals, 
and  the  group  may  be  appropiately  termed  the  platinum  group. 
The  whole  group  consists  of  Khodium  (atomic  weight  =  1.04),  Ruthe- 
nium (104),  Palladium  (106.5),  Gold  (196),  Platinum  (197.4),  Indium 
(198),  and   Osmium  (199).      Palladium  is  used  to  impart  to  brass 
gas-fixtures  a  peculiar  reddish  tint,  sometimes  called  salmon-bronze. 
Indium  is  used  for  the  very  hard  tips  of  gold  pens.      Osmium 
forms,  among  other  oxides,  a  volatile  compound  OsO4,  whose  vapors 
are  intensely  poisonous.     The  metals  of  this  group  are  noble  metals  ; 
they  withstand  the  action  of  the  atmosphere  ;   none  of  them  are 
acted  upon  by  nitric  acid,  though  they  dissolve  in  chlorine  and  in 
aqua  regia.     Their  oxides  part  with  all  their  oxygen  when  simply 
heated,  leaving  the  metal  behind. 


286  EQUIVALENT   WEIGHTS.  [§  513. 

513.  Equivalent  Weights.  —  In  experiments  like  Exp.  204,  §  442, 
where  one  metal  replaces  another,  it  is  found  that  the  replacement 
always  occurs  in  fixed  and  definite  proportions.  In  this  particular 
experiment  the  amount  of  lead  deposited  was  to  the  amount  of  zinc 
dissolved  as  103.5  to  32.5.  If  a  solution  of  a  salt  of  silver  had  been 
employed  instead  of  the  lead  acetate,  the  amount  of  silver  deposited 
would  have  been  to  the  zinc  dissolved  as  108  to  32.5.  The  weights 
of  the  metals  thus  deposited  or  dissolved,  that  is  to  say,  the  amounts 
indicated  by  the  numbers  103.5  and  32.5  in  the  case  of  lead  and  zinc, 
may  be  said  to  be  the  equivalents  of  each  other  :  these  numbers  (or 
others  bearing  the  same  relation  to  each  other)  may  be  called  the 
equivalent  weights  of  lead  and  zinc  respectively.  The  number  of  ele- 
ments whose  equivalent  weights  can  be  thus  determined  by  the  actual 
replacement  of  one  by  the  other  is  limited,  but  even  in  cases  where 
two  elements  do  not  replace  each  other,  their  equivalent  weights  may 
still  be  determined  by  comparing  each  of  the  two  elements  with  a 
third.  In  this  way,  by  direct  or  by  indirect  means,  we  may  draw  up 
a  table  of  the  "  equivalent  weights  "  of  the  different  elements  ;  these 
equivalent  weights  would  be  either  the  same  as  the  atomic  weights,  or 
some  simple  multiple  or  submultiple  of  them,  for  by  the  very  concep- 
tion of  the  atomic  theory  no  replacement  could  take  place  except  by  a 
certain  number  of  whole  atoms. 

In  many  works  on  chemistry  the  student  will  find  assigned  to  sev- 
eral of  the  chemical  elements  other  weights  than  those  given  on  page 
295.  Thus,  it  was  customary  at  one  time  to  assign  the  weight  16  to 
sulphur  instead  of  32,  8  to  oxygen  instead  of  16,  etc.  These  weights 
are  the  equivalent  weights  just  described,  and  they  are  still  often  used 
by  persons  devoted  to  the  practical  applications  of  chemistry.  The 
reasons  which  have  led  to  the  adoption  of  the  series  of  atomic  weights 
in  present  use  cannot  be  appropriately  discussed  in  this  manual  .*  For 
most  purposes  of  calculation  it  is  immaterial  whether  the  "  equiva- 
lent "  or  the  "  atomic"  weights  be  employed.  Thus  water  is  made  up 
of  1  part  by  weight  of  hydrogen  and  8  parts  by  weight  of  oxygen  ; 
and  it  was  formerly  the  custom  to  represent  the  equivalent  weight  of 
oxygen  (8)  by  the  symbol  O.  On  this  system  the  symbol  HO  stood 
for  water,  and  indicated  that  water  contains  hydrogen  and  oxygen  in 
the  proportion  of  1  to  8,  and  that  its  equivalent  weight  is  9.  But 
since  the  molecule  of  water  is  held  to  contain  two  atoms  of  hydrogen 

*  See  Eliot  and  Storer's  Manual  of  Inorganic  Chemistry,  pp.  603  and  fol- 
lowing. 


§  514.]  EQUIVALENT   WEIGHTS.  287 

and  one  atom  of  oxygen,  the  atom  of  oxygen  weighing  16,  the  symbol 
of  the  compound  is  written  H2O.  The  proportion  of  hydrogen  to 
oxygen  is  in  both  cases  the  same  ;  and,  in  general,  it  is  evident  that 
the  relative  proportion  in  which  any  two  or  more  elements  exist  in  a 
chemical  compound  is  a  matter  of  fact  determined  by  analysis  :  it  is 
something  which  no  theoretical  conceptions  of  ours  can  change.  The 
atomic  weights,  however,  or  the  values  which  we  assign  to  the  symbols 
of  the  elements,  must  be  fixed  by  what  we  hold  to  be  true  with  regard 
,to  the  number  of  atoms  in  the  molecule  of  the  compound.  It  is  a 
better  knowledge  of  the  molecular  constitution  of  bodies  than  was 
accessible  to  their  predecessors  that  has  led  the  chemists  of  the  present 
day  to  employ  new  atomic  weights  in  the  case  of  a  considerable  num- 
ber of  the  elements.  The  more  common  elements  whose  atomic 
weights  are  double  the  equivalent  weights  formerly  assigned  to  them 
are  as  follows  :  — 

-     ALUMINUM,  IRON,  PLATINUM, 

BARIUM,  LEAD,  SELENIUM, 

CADMIUM,  MAGNESIUM,  SILICON, 

CALCIUM,  MANGANESE,  STRONTIUM, 

CARBON,  MERCURY,  SULPHUR, 

CHROMIUM,  NICKEL,  TIN, 

COBALT,  OXYGEN,  URANIUM, 

COPPER,  PALLADIUM,  ZINC. 

In  passing,  then,  from  the  formulae  of  the  older  system  to  the  cor- 
responding formulae  of  the  new,  if  the  atomic  weight  of  any  element 
is  double  the  old  equivalent  weight,  it  becomes  necessary,  in  writing 
the  symbol  of  any  molecule  containing  this  element,  either  to  take 
half  as  many  atoms  of  the  element  in  question  or  to  take  twice  as 
many  atoms  of  the  other  elements  in  the  molecule  unless  they  also 
have  had  their  combining  weights  doubled.  Thus  the  symbol  of  the 
ordinary  platinum  chloride  was  formerly  written  Pt  C12 ;  now,  since 
the  combining  weight  of  platinum  is  regarded  as  197.4  instead  of  98.7, 
as  formerly,  the  symbol  must  be  written  Pt  C14,  in  order  to  express 
the  same  relative  proportion  of  chlorine  and  platinum. 

514.  Nomenclature.  —  In  connection  with  the  adoption  of  the 
atomic  weights  now  in  use,  although  not  logically  dependent  upon  it, 
there  have  occurred  certain  changes  of  nomenclature,  especially  in 
regard  to  the  salts  .of  the  ordinary  acids.  The  term  acid  itself  is  not 
used  in  the  same  sense  as  formerly.  Now  (see  pages  41  -  43)  we  are 
inclined  to  restrict  the  term  acid  to  bodies  containing  hydrogen  which 


288  NOMENCLATURE.  [§  515. 

can  be  replaced  by  a  metallic  element  ;  it  was  formerly  applied  also 
to  bodies  which  in  this  book  have  been  called  anhydrides.  Thus 
SOS  was  called  sulphuric  acid  (or  anhydrous  sulphuric  acid),  and 
H2SO4  was  regarded  as  a  compound  of  SO3  and  water,  and  written 
H2O,  SO3.  In  like  manner  the  sulphates  were  regarded  as  com- 
pounds of  SO8  with  the  oxides  of  the  metallic  elements,  and  were 
named,  in  accordance  with  this  idea,  sulphate  of  soda,  sulphate  of 
lime,  etc.,  instead  of  sulphate  of  sodium,  sulphate  of  calcium,  etc. 
There  is  at  the  present  time,  however,  no  uniformity  of  nomenclature. 
Some  chemists  say  sulphate  of  sodium,  some  say  sodium  sulphate, 
others  say  sodic  sulphate  ;  while  the  old  term  sulphate  of  soda  con- 
tends with  them  and  with  the  still  older  term,  Glauber's  salt,  for  a 
place  in  the  language  of  commerce,  of  literature,  and  of  ordinary  life. 
As  a  rule,  when  there  are  two  series  of  salts  derived  from  the  same 
element,  it  is  usual  to  distinguish  between  the  two  by  the  use  of  the 
terminations  -ous  and  -ic,  as,  for  example,  ferrous  sulphate  and  ferric 
sulphate. 

In  the  designation  of  the  so-called  binary  compounds  (i.  e.  com- 
pounds of  two  elements  only)  there  is  the  same  diversity  of  practice  ; 
thus  the  names  soda,  oxide  of  sodium,  sodium  oxide,  and  sodic  oxide 
are  all  applied  to  the  same  compound  of  oxygen  and  sodium.  Where 
there  are  two  oxides  of  the  same  element  (or  chlorides,  sulphides,  etc.), 
the  terminations  -ous  and  -ic  are  sometimes  employed  ;  more  gener- 
ally, however,  prefixes,  either  Latin  or  Greek,  are  used  :  thus,  when 
the  molecule  of  an  oxide  contains  only  one  atom  of  oxygen  it  is  called 
the  protoxide  or  monoxide ;  when  there  are  two  atoms  of  oxygen  in  the 
molecule,  it  is  called  the  binoxide  or  di-oxide  ;  succeeding  compounds 
would  be  the  teroxide  or  trioxide,  quadroxide  or  tetroxide,  etc.  (see 
page  37). 

515.  Quantivalence. — In  addition  to  the  statements  of  §  74,  it  may 
be  remarked  that  the  atom  of  the  same  element  does  not  always  possess 
the  same  quantivalence.  Thus,  while  the  quantivalence  of  hydrogen 
is  always  taken  as  1,  and  that  of  oxygen  as  2,  the  quantivalence  of 
sulphur  is  sometimes  6,  sometimes  4,  and  sometimes  2,  that  of  nitrogen 
is  sometimes  5  and  sometimes  3.  As  a  rule,  when  an  element  varies 
in  quantivalence,  the  various  degrees  of  quantivalence  possible  to  the 
same  atom  are  either  all  odd  or  all  even. 

We  do  not  know  to  what  the  observed  difference  in  the  combining 
power  of  the  different  atoms  is  due.  In  order,  however,  to  represent 
it  to  the  eye,  it  is  usual  to  attach  to  the  symbol  of  the  atom  of  an 
element  as  many  dashes  as  will  indicate  the  quantivalence.  If  com- 


$  515.]  QUANTIVALENCE.  289 

bination  takes  place  between  elementary  atoms  of  two  kinds,  the 
total  quatitivalence  of  each  element  must  be  the  same.  If  this  be  ex- 
pressed graphically,  the  number  of  dashes  attached  to  each  symbol, 
or,  as  is  often  said,  the  number  of  bonds  must  be  the  same.  Thus,  in 
H  —  Cl  we  have  represented  the  union  of  2  univalent  atoms  ;  in 
H  —  O  —  H  the  union  of  one  bivalent  with  two  univalent  atoms.  If 
a  compound  is  made  up  of  atoms  of  more  than  two  kinds,  it  is  still 
possible  to  write  the  symbol  graphically,  so  as  to  represent  each  atom 
as  united  to  other  atoms  by  all  the  bonds  attached  to  it  to  indicate 
its  quantivalence.  Thus,  H2SO4  and  AgNO3  may  be  written 

O  O 

H  —  O  —  S—  O—  H  Ag  —  O  —  N 


u 


In  these  symbols  the  atoms  are  represented,  H  and  Ag  as  univalent, 
O  as  bivalent,  N  as  quinquivalent,  and  S  as  hexivalent.  No  mol- 
ecule can  exist,  by  this  theory,  in  which  the  atoms  must  be  repre- 
sented with  bonds  unconnected  with  other  atoms  :  thus  there  could 
be  no  such  molecule  as  HO,  for  if  written  graphically,  H  —  O  —  , 
it  is  seen  that  the  oxygen  is  "  unsatisfied."  Such  a  group  of  atoms  is 
called  a  compound  radical,  and  the  number  of  bonds  unsatisfied 
is  the  quantivalence  of  the  radical.  Thus  HO  —  is  a  univalent  rad- 
ical, while  H  —  O  —  H,  H  —  O  —  O  —  H  (hydrogen  peroxide), 
H  —  O  —  Ca  —  O  —  H  (calcium  hydrate)  are  satisfied  or  "  satu- 
rated" molecules.  This  shows  how  it  is  possible  for  the  single 
atom  of  copper  to  be  bivalent  (  —  Ou  —  )  and  for  the  group  of  two 
atoms  to  form  a  bivalent  combination  —  (Cu  —  Cu)  —  .  This 
grouping  of  the  atoms  together  is  not  an  arbitrary  matter  of  the  na- 
ture of  a  "dissected  map."  In  the  arrangement  of  the  atoms  it  is 
not  simply  a  question  of  so  linking  the  atoms  together  that  the  con- 
ditions implied  by  the  quantivalence  of  the  atoms  shall  be  satisfied  ; 
such  formulae  attempt  also  to  represent,  in  some  sense  the  structure  of 
the  molecule,  at  least  so  far  as  to  indicate  the  relations  which  we  be- 
lieve to  exist  among  the  various  atoms  which  compose  it  ;  this  is, 
however,  a  matter  not  sufficiently  elementary  in  its  character  to  be 
considered  in  this  place.  Undue  stress  is  laid  upon  this  matter  of 
quantivalence  by  many  chemists  ;  but  the  theory  expresses,  although 
in  a  rather  crude  way,  relations  which  actually  exist,  and  although  it 


290  OXIDATION  AND  REDUCTION.  [§  516. 

may,  and  probably  will,  be  displaced  by  some  other  theory  which  will 
explain  the  same  facts  in  a  more  satisfactory  manner,  it  has  been,  and 
is,  of  great  value.  To  the  beginner  it  is  chiefly  valuable  for  the  aid 
afforded  in  writing  formulae  and  equations.  The  graphical 
formulae  and  equations  written  in  accordance  with  this  theory,  are 
useful,  chiefly  because  they  can  be  made  to  represent  more  facts  and 
more  suppositions  than  can  be  expressed  in  ordinary  formulae  and 
equations. 

The  term  atomicity  is  applied  to  the  highest  degree  of  quantiva- 
lence  which  the  same  atom  may  possess  ;  and  the  atoms  are  desig- 
nated as  monads,  dyads,  triads,  tetrads,  pentads,  hexads  and  heptads, 
according  as  the  atomicity  is  one,  two,  three,  four,  five,  six,  or  seven. 
These  terms,  monad,  dyad,  etc.,  are  sometimes  used,  however,  to 
denote  the  more  common  degree  of  quantivalence,  rather  than  the 
highest  which  the  atom  is  capable  of  exhibiting.  Thus  the  atomicity 
of  lead  is  four  ;  its  prevailing  quantivalence  is  two  ;  lead  would  thus, 
according  to  the  first  plan,  be  spoken  of  as  a  tetrad,  according  to  the 
second  as  a  dyad. 

516.  Oxidation  and  Reduction. — The  terms  oxidation  and  reduc- 
tion are  used  in  a  much  wider  sense  than  is  implied  in  §  129  on  page 
81,  although  the  simplest  use  is  as  there  indicated.  As  an  example  of 
another  use  of  the  terms  we  may  take  the  case  of  the  two  chlorides  of 
tin.  If  by  some  chemical  process  the  stannows  oxide  (SnO)  were  con- 
verted into  the  stannic  oxide  (SnOa),  we  should  legitimately  speak  of 
this  as  a  process  of  oxidation  ;  if,  now,  the  stannows  chloride  (SnCl2) 
in  which  the  atom  of  tin,  as  in  stannous  oxide,  is  bivalent,  be  con- 
verted into  the  stannic  chloride  (SnCl4),  in  which  the  atom  of  tin,  as 
in  stannic  oxide,  is  quadrivalent,  we  speak  of  this  process  also  as  one 
of  oxidation,  although  there  is  no  oxygen  in  either  compound.  If  the 
reverse  action  were  performed,  and  the  stannic  chloride  were  converted 
into  the  stannous  chloride,  we  should  speak  of  the  process  as  one  ol 
reduction.  The  ferrous  compounds  are  converted  into  the  ferric  com- 
pounds, the  salts  of  chromiuni  into  chromates,  the  mercurous  salts  into 
mercuric,  and  so  on,  by  oxidizing  agents,  and,  in  general,  where  an 
element  can  occur  with  two  different  degrees  of  quantivalence ,  the  passing 
from  the  lower  to  the  higher  is  hrought  about  by  an  oxidizing  action,  the 
passing  from  the  higher  to  the  lower  ~by  a  reducing  action.  No  objection 
can  be  made  to  the  use  of  the  terms  reduction  and  reducing  agent  in 
this  connection  ;  the  terms  oxidation  and  oxidizing  agent  are,  in  some 


§  517.]  OXIDATION  AND  REDUCTION.  291 

cases,  manifestly  improper,  although  still  often  used.  Such  use  of  the 
terms  originated  when  the  dualistic  idea  that  the  salts  contained  the 
corresponding  oxides  was  generally  accepted,  and  from  such  salts  as 
sulphates,  etc.,  the  use  was  extended  even  to  chlorides. 

Other  characteristic  examples  of  oxidizing   and   reducing  actions 
are  as  follows  : — 

(p.  152)  C2H5,  HO  +  O  =  C2H3O,  H  +  H2O, 

Alcohol.  Aldehyde. 

Here  the  aldehyde  contains  no  more  oxygen  than  the  alcohol,  but  it 
contains  less  hydrogen,  a  portion  of  the  hydrogen  having  been  oxi- 
dized and  removed  as  water. 

(p.  200)  C16H,oN2O2  +  H2  =  Ci6Hi2N2O2. 

Indigo  blue.  Reduced  indigo. 

Here  the  hydrogen  acts  as  a  reducing  agent,  not  by  appropriating 
oxygen,  but  by  actually  entering  into  the  molecule.  When  the  re- 
duced or  white  indigo  is  exposed  to  the  air  it  becomes  blue.  The 
white  indigo  is  said  to  be  oxidized,  although  the  action  is  really  a 
removal  of  hydrogen,  as  seen  in  the  following  equation  : — 

Ci6Hi2N2O2  +  O  —  Ci6Hi0N2O2  +  H2O. 
Reduced  indigo.  Indigo  blue. 

Chlorine  is  often  spoken  of  as  an  oxidizing  agent ;  it  acts  in  two 
distinct  ways,  which  may  be  illustrated  as  follows  : — 

Hg2Cl2  +  2  Cl  =  2  HgCl2. 
3  H2O,  As2O3  +  2  H2O  +  4  Cl  =  3  H2O,  As2O5  +  4  HC1. 

Arsenious  acid.  Arsenic  acid. 

In  the  first  equation  chlorine  enters  into  the  compound  oxidized ; 
the  mercurous  chloride  is  said  to  be  "  oxidized  "  to  mercuric  chloride. 
In  the  second  equation  the  chlorine  acts  by  appropriating  the  hy- 
drogen of  two  molecules  of  water,  leaving  the  oxygen  free  to  enter 
into  combination. 

517.  Volumetric  interpretation  of  symbols. — We  have  already 
seen  (page  88)  that  all  gaseous  molecules  are  believed,  under  like  con- 
ditions, to  occupy  the  same  space  ;  consequently,  the  symbols  for  all 
molecules  may  be  taken  to  represent  equal  volumes  of  the  substances 
indicated,  and  by  general  agreement  the  symbol  of  a  molecule  when 
used  to  express  volumetric  relations  always  stands  for  two  volumes. 
The  symbols  of  the  individual  elements,  as  H,  O,  N,  etc.,  we  have 
already  used  to  represent,  1st,  an  atom  of  the  element,  and  2d,  a 


292        VOLUMETRIC  INTERPRETATION  OF  SYMBOLS.     [§518. 

certain  number  of  parts  by  weight  of  the  elementary  substance, 
namely,  that  number  of  parts  which  is  indicated  by  the  combining  or 
atomic  weight.  The  same  symbol  may  be  also  used  to  denote  (3d) 
a  certain  volume  of  the  element  in  question,  when  that  element  is  in 
the  gaseous  state.  We  have  already  used  (page  18  and  often)  the 
symbols  H,  O,  N,  and  S,  to  denote  one  volume  of  hydrogen,  oxygen, 
nitrogen  and  sulphur  (vapor),  respectively,  and,  in  general,  when  the 
element  is  one  whose  molecule  contains  two  atoms,  the  symbol  for  the 
atom  is  used  to  indicate  one  volume.  When  the  element  is  one  whose 
molecule  contains  only  one  atom,  the  symbol' for  the  atom  will  be 
also  the  symbol  of  the  molecule,  and  will  denote  two  volumes  : — 
thus,  Hg  denotes  two  volumes  of  mercury  vapor.  When  the  ele- 
ment is  one  whose  molecule  contains  4  atoms,  the  symbol  for  the 
atom  will  indicate  only  half  a  volume  : — thus,  P  stands  for  only 
half  a  volume  of  phosphorus  vapor.  Examples  of  the  volumetric 
interpretation  of  symbols  are  found  on  pages  34,  37,  46,  97,  and  others. 
As  the  great  majority  of  the  known  elements  cannot  be  volatilized, 
or  made  gaseous,  by  the  highest  temperatures  as  yet  at  our  command, 
under  conditions  which  permit  the  chemist  to  experiment  with  the 
gases  produced,  it  is  plain  that  the  composition  by  weight  is,  in  the 
present  state  of  chemistry,  of  far  greater  practical  importance  than 
composition  by  volume. 

518.  Coincidence  of  Atomic  Weight  and  Unit- Volume 
Weight. — The  specific  gravity  of  a  gas  or  vapor  is  the  weight 
of  any  volume  of  that  gas  or  vapor  as  compared  with  the  weight 
of  the  same  volume  of  hydrogen  gas  under  like  conditions  of  tem- 
perature and  pressure  ;  we  use  the  term  vapor  density  to  de- 
note the  same  idea,  and,  less  commonly,  the  term  unit-volume 
•weight.  The  same  number  expresses  both  the  vapor  density  and 
the  atomic  weight  in  the  case  of  those  elements  mentioned  on  p.  91, 
whose  molecules  contain  each  two  atoms.  Of  course,  this  coinci- 
dence is  something  that  is  established  by  experimental  observation  ; 
it  does  not  follow  from,  but  actually  is  a  part  of  the  basis  of,  our 
theory  as  to  the  constitution  of  the  molecules  in  question.  In  the 
case  of  the  elements  whose  molecules  contain  four  atoms  each,  the 
vapor  density  will  be  twice  the  atomic  weight,  and  in  the  case  of  the 
elements  whose  molecules  contain  one  atom  each,  the  vapor  density 
will  be  one-half  the  atomic  weight. 

It  is  not  necessary  to  suppose  that  the  same  elementary  substance 


§  519.]  ELECTRO-CHEMICAL  RELATIONS.  293 

always,  and  under  all  conditions,  contains  the  same  number  of  atoms 
in  the  molecule.  In  the  first  place  it  is  only  when  the  elementary 
substances  are  gaseous  that  we  have,  at  present,  means  for  arguing 
as  to  the  constitution  of  their  molecules.  The  molecule  of  sulphur  in 
the  gaseous  state,  contains  two  atoms,  but  in  the  solid  state  it  may 
contain  more  than  two.  In  fact,  the  phenomena  of  allotropism  are 
best  explained  by  supposing  either  that  the  various  modifications 
have  a  different  number  of  atoms  in  the  molecule,  or  that  there  is 
some  difference  in  the  arrangement  of  these  atoms.  In  the  case  of 
ozone  there  is  good  reason  to  suppose  that  the  molecule  contains 
3  atoms,  while  the  molecule  of  oxygen  contains  only  2,  as  already 
stated  on  page  70. 

519.  Electrical  Relations  of  the  Atoms. — [To  accompany  page 
257.]  Speaking  somewhat  loosely,  all  the  elements  which  in  this  list 
precede  gold  are  negative,  while  gold  and  the  elements  which  follow 
it  are  positive.  We  have  been  in  the  habit  of  speaking  of  the  nega- 
tive elements  collectively  as  the  non-metallic  elements.  The  terms 
negative  and  positive  are,  on  some  accounts,  to  be  preferred,  al- 
though themselves  not  perfectly  exact  in  their  signification.  The 
same  element  in  different  compounds  will  often  play  a  very  dif- 
ferent part.  Thus  the  element  zinc,  which  we  are  now  studying, 
acts  in  its  compounds  ordinarily  as  a  positive  element ;  its  hy- 
drate (ZnH2O-2)  is  a  base,  its  oxide  (ZnO)  is  a  basic  anhydride, 
and  the  element  when  in  combination  is  usually  combined  with 
negative  elements  or  radicals,  as,  for  example,  in  ZnCl->,  ZnSO4, 
etc.  Occasionally,  however,  zinc  plays  the  part  of  a  negative  ele- 
ment, as,  for  instance,  in  potassium  zincate  (Exp.  202).  In  this 
compound  the  zinc  plays  the  same  part  that  sulphur  does  in  the 
sulphates,  nitrogen  in  the  nitrates,  etc.  Corresponding  to  potas- 
sium zincate  (K2Oi>Zn),  we  should  have  zincic  acid  (HiOi-Zn)  and 
zincic  anhydride  (ZnO).  In  fact,  the  hydrate  of  zinc  does  dis- 
solve, either  in  acids  (acting,  therefore,  as  a  base)  or  in  alkalies 
(acting  as  an  acid).  Many  of  the  elements  which  we  generally 
designate  as  positive  or  metallic,  act  in  a  similar  manner ;  this 
difference  of  action  is  often  accompanied  by  difference  in  quan- 
tivcdence.  Thus  in  the  case  of  chromium,  we  have  two  very  dis- 
tinct classes  of  compounds  ;  1st,  the  salts  of  chromium,  in  which 
we  recognize  the  double  atom  of  chromium,  Cr2,  acting  as  a  hex- 
ivalent  positive  radical;  2d,  the  chromates  of  various  elements  in 


294  ELECTRO-CHEMICAL  RELATIONS. 

which  the  single  atom  of  chromium,  Cr,  is  hexivalent  and  neg- 
ative. Corresponding  to  the  former  of  these  two  classes  we  have 
the  basic  oxide,  CraOa,  and  the  basic  hydrate,  Cr2H6O6 ;  corres- 
ponding to  the  second  class  we  have  the  acid  anhydride  CrOs  and 
the  acid 


ATOMIC   WEIGHTS  OF  THE  ELEMENTS. 


295 


CHAPTEE  XXX. 
ATOMIC  WEIGHTS  OF  THE  ELEMENTS. 

AN  alphabetical  list  of  the  sixty-four  recognized  elements, 
with  their  symbols  and  atomic  weights,  is  here  given  for  con- 
venience of  reference.  The  names  of  the  rarer  elements  which 
are  at  present  of  little  importance  are  printed  in  italics  :  — 


Aluminum,  . 

.     Al 

.     27.4 

Mercury, 

•     Hg 

.  200 

Antimony,    . 

.     Sb 

.  120 

Molybdenum, 

.     Mo 

.     96 

Arsenic, 

.     As 

.     75 

Nickel, 

.     Ni 

.     58.8 

Barium, 

.     Ba 

.  137 

Nitrogen, 

.     N 

.     14 

Bismuth, 

.     Bi 

.  210 

Osmium, 

.     Os 

.  199 

Boron, 

.     B 

.     11 

Oxygen, 

.     0 

.     16 

Bromine, 

.     Br 

.     80 

Palladium,    . 

.     Pd 

.  106.5 

Cadmium,     . 

.     Cd 

.  112 

Phosphorus,  . 

.     P 

.     31 

Ccesium, 

.     Cs 

.  133 

Platinum, 

.     Pt 

.  197.4 

Calcium, 

.     Ca 

.     40 

Potassium,    . 

.     K 

.     39.1 

Carbon, 

.     C 

.     12 

Rhodium, 

.     Rh 

.  104 

Cerium, 

.     Ce 

.     92 

Rubidium,     . 

.     Rb 

.     85.7 

Chlorine, 

.     Cl 

.     35.5 

Ruthenium,   . 

.     Ru 

.  104 

Chromium,   . 

.     Cr 

.     52.5 

Selenium, 

.     Se 

.     79.5 

Cobalt,  . 

.     Co 

.     58.8 

Silicon, 

.     Si 

.     28 

Columbium,  . 

.     Cb 

.     94 

Silver,  . 

.     Ag 

.  108 

Copper, 

.     Cu 

.     63.4 

Sodium, 

.     Na 

.     23 

Didymium,    . 

.     D 

.     95 

Strontium,     . 

.     Si 

.     87.5 

Erbium, 

.     E 

.  112.6 

Sulphur, 

.     S 

.     32 

Fluorine, 

.     F 

.     19 

Tantalum, 

.     Ta 

.  182 

Glucinum,     . 

.     Gl 

.     14 

Tellurium,     . 

.     Te 

.  128 

Gold,    . 

.     Au 

.  196 

Thallium,      -.  > 

.     Tl 

.  2Q4 

Hydrogen,    . 

H 

1 

Thorium, 

.     Th 

.  231.4 

Indium, 

.     In 

.  113.4 

Tin, 

.     Sii 

.  118 

Iodine, 

.     I 

.  127 

Titanium,      . 

.     Ti 

.     50 

Iridium, 

.     Ir 

.  198 

Tungsten, 

.     W 

.  184 

Iron,     . 

.     Fe 

.     56 

Uranium, 

.     Ur 

.  120 

Lanthanum,  . 

.     La 

.     93 

Vanadium,    . 

.     V 

.     51.3 

Lead,    . 

.     Fb 

.  207 

Yttrium, 

.     Yt 

.     61.6 

Lithium, 

.     Li 

.      7 

Zinc, 

.     Zii 

.     65 

Magnesium,  . 

.     Mg 

.     24 

Zirconium,    . 

.    Zr 

.     89.6 

Manganese,  . 

.     Mn 

.     55 

Gallium, 

.     Oa 

.     69.8 

296 


CLASSIFICATION  OF  THE  ELEMENTS. 


In  the  following  list  the  more  important  of  the  elements 
are  arranged  in  the  groups  in  which  they  have  been  studied 
in  the  preceding  pages.  Without  accepting  any  one  infallible 
criterion  of  classification,  or  insisting  upon  any  systematic  ar- 
rangement of  the  elements  in  groups  with  that  strenuousness 
which  is  apt  to  make  classification  rather  a  hindrance  than  a 
help,  the  student  may  provisionally  use  this  subdivision  of  the 
elements  into  groups,  as  a  help  in  remembering  facts,  as  a 
guide  to  the  prompt  recognition  of  general  properties  and  gen- 
eral laws,  and  as  a  suggestive  compend  of  his  whole  chemical 
knowledge  :  — 


Fluorine,     . 

.     19 

Calcium,     . 

.     40 

Chlorine,     . 

.     35.5 

Strontium,  . 

.     87.5 

Bromine 

.     80 

.  137 

Iodine, 

.  127 

Lead, 

.  207 

Oxygen,      . 

.     16 

Magnesium, 

.    '24 

Sulphur,     . 

.     32 

Zinc,  . 

.         .     65 

.     79.5 

Cadmium,  . 

.   112 

Tellurium,  . 

.  128 

- 

Glucinum,  . 

.     14 

Nitrogen,    . 

.     14 

Aluminum, 

.     27.4 

Phosphorus, 

.     31 

Chromium, 

.     52.5 

Arsenic, 

.     75 

Manganese, 

.     55 

Antimony,  . 

.  120 

Iron,  . 

.     56 

Bismuth,     . 

.  210 

Cobalt, 

.     58.8 

Nickel, 

.     58.8 

Carbon, 

.     12 

Uranium,   . 

.  120 

Boron, 

.     11 

Silicon,    <    . 

.     28 

Copper, 

.     63.4 

Mercury,     . 

.  200 

Hydrogen,  . 

.       1 

Lithium, 

7 

Tin,    .         . 

.  118 

Sodium, 

...         .23 

T'n'f'nQd'i  m~n 

39.1 

Gold  . 

.  196 

JT  U  Lclool  Lllllj  . 

Silver, 

.  108 

Platinum,  . 

.  197.4 

APPENDIX. 


CHEMICAL   MANIPULATION. 

1.  Glass-tubing.  —  Two  qualities  of  glass-tubing  are  used  in  chem- 
ical experiments,  —  that  which  softens  readily  in  the  flame  of  a  gas-  or 
spirit-lamp,  and  that  which  fuses  with  extreme  difficulty  in  the  flame 
of  the  blast-lamp.  These  two  qualities  are  distinguished  by  the 
terms  soft  and  hard  glass.  Soft  glass  may  be  used  for  all  purposes, 
except  the  intense  heating,  or  ignition,  of  dry  substances.  Fig.  I 
represents  the  most  convenient  sizes  of  glass-tubing,  both  hard  and 
soft,  and  shows  also  the  proper  thickness  of  the  glass  walls  for  each 
size. 

FIG.  I. 


2.  Cutting  and  Cracking  Glass.  —  Glass-tubing  and  glass-rod 
must  generally  be  cut  to  the  length  required  for  any  particular  ap- 
paratus. A  sharp  triangular  file  is  used  for  this  purpose.  The  stick 
of  tubing,  or  rod,  to  be  cut  is  laid  upon  a  table,  and  a  deep  scratch  is 
made  with  the  file  at  the  place  where  the  fracture  is  to  be  made.  The 
stick  is  then  grasped  with  the  two  hands,  one  on  each  side  of  the 
25 


ji  APPENDIX, 

mark,  while  the  thumbs  are  brought  together  just  at  the  scratch.  By 
pushing  with  the  thumbs  and  pulling  in  the  opposite  direction  with 
the  fingers,  the  stick  is  broken  squarely  at  the  scratch,  just  as  a  stick 
of  candy  or  a  dry  twig  may  be  broken.  The  sharp  edges  of  the  fracture 
should  invariably  be  made  smooth,  either  with  a  wet  file,  or  by  soften- 
ing the  end  of  the  tube  or  rod  in  the  lamp.  (See  Appendix,  §  3.) 
Tubes  or  rods  of  sizes  4  to  8  inclusive  may  readily  be  cut  in  this  man- 
ner ;  the  larger  sizes  are  divided  with  more  difficulty,  and  it  is  often 
necessary  to  make  the  file-mark  both  long  and  deep.  An  even  frac- 
ture is  not  always  to  be  obtained  with  large  tubes.  The  lower  ends 
of  glass  funnels,  and  those  ends  of  gas  delivery-tubes  which  enter  the 
bottle  or  flask  in  which  the  gas  is  generated,  should  be  filed  off,  or 
FIG.  H.  ground  off  on  a  grindstone,  obliquely  (Fig.  II),  to 

facilitate  the  dropping  of  liquids  from  such  extremi- 
ties. 

In  order  to  cut  glass  plates,  the  glazier's  diamond 
must  be  resorted  to.  For  cutting  exceedingly  thin 
glass  tubes  and  other  glass  ware,  like  flasks,  retorts 
and  bottles,  still  other  means  are  resorted  to,  based  upon  the  sudden 
and  unequal  application  of  heat.  The  process  divides  itself  into 
two  parts,  the  producing  of  a  crack  in  the  required  place,  and  the 
subsequent  guiding  of  this  crack  in  the  desired  direction.  To  pro- 
duce a.  crack,  a  scratch  must  be  made  with  the  file,  and  to  this  scratch 
a  pointed  bit  of  red-hot  charcoal,  or  the  jet  of  flame  produced  by 
the  mouth  blowpipe,  or  a  very  fine  gas-flame,  or  a  red-hot  glass-rod 
may  be  applied.  If  the  heat  does  not  produce  a  crack,  a  wet  stick  or 
file  may  be  touched  upon  the  hot  spot.  Upon  any  part  of  a  glass  sur- 
face except  the  edge,  it  is  not  possible  to  control  perfectly  the  direc- 
tion and  extent  of  this  first  crack  ;  at  an  edge  a  small  crack  may  be 
started  with  tolerable  certainty  by  carrying  the  file-mark  entirely  over 
the  edge.  To  guide  the  crack  thus  started,  a  pointed  bit  of  charcoal 
or  slow-match  may  be  used.  The  hot  point  must  be  kept  on  the  glass 
from  1  c.  m.  to  0.5  c.  m.  in  advance  of  the  point  of  the  crack.  The 
crack  will  follow  the  hot  point,  and  may  therefore  be  carried  in  any 
desired  direction.  By  turning  and  blowing  upon  the  coal  or  slow- 
match,  the  point  may  be  kept  sufficiently  hot.  Whenever  the  place 
of  experiment  is  supplied  with  common  illuminating  gas,  a  very  small 
jet  of  burning  gas  may  be  advantageously  substituted  for  the  hot  coal 
or  slow  match.  To  obtain  such  a  sharp  jet,  a  piece  of  hard  glass 
tube,  No.  5,  10  c.  m.  long,  and  drawn  to  a  very  fine  point  (see  Ap- 


APPENDIX,  iii 

pendix,  §  3),  should  be  placed  in  the  caoutchouc  tube  which  ordinarily 
delivers  the  gas  to  the  gas-lamp,  and  the  gas  should  be  lighted  at  the 
fine  extremity.  The  burning  jet  should  have  a  fine  point,  and  should 
not  exceed  1.5  c.  m.  in  length.  By  a  judicious  use  of  these  simple 
tools,  broken  tubes,  beakers,  flasks,  retorts  and  bottles  may  often  be 
made  to  yield  very  useful  articles  of  apparatus.  No  sharp  edges 
should  be  allowed  to  remain  upon  glass  apparatus.  The  durability 
of  the  apparatus  itself,  and  of  the  corks  and  caoutchouc  stoppers  and 
tubing  used  with  it,  will  be  much  greater,  if  all  sharp  edges  are  re- 
moved with  the  tile,  or,  still  better,  rounded  in  the  lamp. 

3.  Bending  and  Closing  Glass-tubes.  —  Tubing  of  sizes  5 
to  8  inclusive  can  generally  be  worked  in  the  common  gas-  or  spirit- 
lamp  ;  for  larger  tubes  the  blast-lamp  is  necessary  (see  Appendix, 
§  6).  Glass  tubing  must  not  be  introduced  suddenly  into  the  hottest 
part  of  the  flame,  lest  it  crack.  Neither  should  a  hot  tube  be  taken 
from  the  flame  and  laid  at  once  upon  a  cold  surface.  Gradual  heating 
and  gradual  cooling  are  alike  necessary,  and  are  the  more  essential 
the  thicker  the  glass  ;  very  thin  glass  will  sometimes  bear  the  most 
sudden  changes  of  temperature,  but  thick  glass  and  glass  of  uneven 
thickness  absolutely  require  slow  heating  and  annealing.  When  the 
end  of  a  tube  is  to  be  heated,  as  in  rounding  sharp  edges,  more  care  is 
required  in  consequence  of  the  great  facility  with  which  cracks  start 
at  an  edge.  A  tube  should,  therefore,  always  be  brought  first  into  the 
current  of  hot  air  beyond  the  actual  flame  of  the  gas-  or  spirit-lamp, 
and  there  thoroughly  warmed,  before  it  is  introduced  into  the  flame 
itself.  If  a  blast-lamp  is  employed,  the  tube  may  be  warmed  in  the 
smoky  flame,  before  the  blast  is  turned  on,  and  may  subsequently  be 
annealed  in  the  same  manner  ;  the  deposited  soot  will  be  burnt  off  in 
the  first  instance,  and  in  the  last,  may  be  wiped  off  when  the  tube  is 
cold.  In  heating  a  tube,  whether  for  bending,  drawing  or  closing, 
the  tube  must  be  constantly  turned  between  the  fingers,  and  also 
moved  a  little  to  the  right  and  left,  in  order  that  it  may  be  uniformly 
heated  all  around,  and  that  the  temperature  of  the  neighboring  parts 
may  be  duly  raised.  If  a  tube,  or  rod,  is  to  be  heated  at  any  part  but 
an  end,  it  should  be  held  between  the  thumb  and  first  two  fingers  of 
each  hand  in  such  a  manner  that  the  hands  shall  be  below  the  tube,  or 
rod,  with  the  palms  upward,  while  the  lamp-flame  is  between  the 
hands.  When  the  end  of  a  tube,  or  rod,  is  to  be  heated  it  is  best  to 
begin  by  warming  the  tube,  or  rod,  about  2  c.  m.  from  the  end,  and 
from  thence  to  proceed  slowly  to  the  end. 


Iv  APPENDIX. 

The  best  glass  will  not  be  blackened  or  discolored  during  heating. 
The  blackening  occurs  in  glass  which,  like  ordinary  flint  glass,  contains 
lead  (silicate).  Glass  containing  much  lead  is  not  well  adapted  for 
chemical  uses.  The  blackening  may  sometimes  be  removed  by  put- 
ting the  glass  in  the  upper  or  outer  part  of  the  flame,  where  the 
reducing  gases  are  consumed,  and  the  air  has  the  best  access  to  the 
glass.  The  blackening  may  be  altogether  avoided  by  always  keeping 
the  glass  in  the  oxidizing  part  of  the  flame. 

Glass  begins  to  soften  and  bend  below  a  visible  red  heat.  The  con- 
dition of  the  glass  is  judged  of  as  much  by  the  fingers  as  the  eye  ;  the 
hands  feel  the  yielding  of  the  glass,  either  to  bending,  pushing  or 
pulling,  better  than  the  eye  can  see  the  change  of  color  or  form.  It 
may  be  bent  as  soon  as  it  yields  in  the  hands,  but  can  be  drawn  out 
only  when  much  hotter  than  this.  Glass-tubing,  however,  should  not 
be  bent  at  too  low  a  temperature  ;  the  curves  made  at  too  low  a  heat 
are  apt  to  be  flattened,  of  unequal  thickness  on  the  convex  and  con- 
cave sides,  and  brittle. 

In  bending  tubing  to  make  gas  delivery-tubes  and  the  like,  attention 
should  be  paid  to  the  following  points  :  1st,  the  glass  should  be  equally 
hot  on  all  sides  ;  2d,  it  should  not  be  twisted,  pulled  out  or  pushed 
together  during  the  heating  ;  3d,  the  bore  of  the  tube  at  the  bend 
should  be  kept  round,  and  not  altered  in  size  ;  4th,  if  two  or  more 
bends  be  made  in  the  same  piece  of  tubing  (Fig.  Ill,  a),  they  should 
all  be  in  the  same  plane,  so  that  the  finished  tube  will  lie  flat  upon 
the  level  table. 

When  a  tube  or  rod  is  to  be  bent  or  drawn  close  to  its  extremity,  a 
temporary  handle  may  be  attached  to  it  by  softening  the  end  of  the 
tube,  or  rod,  and  pressing  against  the  soft  glass  a  fragment  of  glass 
tube,  which  will  adhere  strongly  to  the  softened  end.  The  handle 
may  subsequently  be  removed  by  a  slight  blow,  or  by  the  aid  of  a  file. 
If  a  considerable  bend  is  to  be  made,  so  that  the  angle  between  the 
arms  will  be  very  small  or  nothing,  as  in  a  siphon,  for  example,  the 
curvature  can  not  be  well  produced  at  one  place  in  the  tube,  but  should 
FIG.  m.  be  made  by  heating,  progressively,  several  cen- 

timetres of  the  tube,  and  bending  continuous- 
ly from  one  end  of  the  heated  portion  to  the 
other  (Fig.  Ill,  6).    Small  and  thick  tube  may 
be  bent  more  sharply  than  large  or  thin  tube. 
In  order  to  draw  a  glass  tube  down  to  a  finer  bore,  it  is  simply 
necessary  to  thoroughly  soften  on  all  sides  one  or  two  centimetres' 


APPENDIX.  v 

length  of  the  tube,  and  then,  taking  the  glass  from  the  flame,  to 
pull  the  parts  asunder  by  a  cautious  movement  of  the  hands.  The 
larger  the  heated  portion  of  glass,  the  longer  will  be  the  tube 
thus  formed.  Its  length  and  fineness  also  increase  with  the  rapidity 
of  motion  of  the  hands.  If  it  is  desirable  that  the  finer  tube 
should  have  thicker  walls  in  proportion  to  its  bore  than  the  origi- 
nal tube,  it  is  only  necessary  to  keep  the  heated  portion  soft  for  two 
or  three  minutes  before  drawing  out  the  tube,  pressing  the  parts 
slightly  together  the  while.  By  this  process  the  glass  will  be  thick- 
ened at  the  hot  ring. 

To  obtain  a  tube  closed  at  one  end,  it  is  best  to  take  a  piece  of 
tubing,  open  at  both  ends,  and  long  enough  to  make  two  closed  tubes. 
In  the  middle  of  the  tube  a  ring  of  glass,  as  narrow  as  possible,  must  be 
made  thoroughly  soft.  The  hands  are  then  separated  a  little,  to  cause 
a  contraction  in  diameter  at  the  hot  and  soft  part.  The  point  of  the 
flame  must  now  be  directed,  not  upon  the  narrowest  part  of  the  tube, 
but  upon  what  is  to  be  the  bottom  of  the  closed  tube.  This  point 
is  indicated  by  the  line  a  in  Fig.  IV.  By  FIG.  iv. 

withdrawing  the  right  hand,  the  narrow  part 
of  the  tube  is  attenuated,  and  finally  melted 
off,  leaving  both  halves  of  the  original  tube 
closed  at  one  end,  but  not  of  the  same  form  ; 
the  right-hand  half  is  drawn  out  into  a  long 

point,  the  other  is  more  roundly  closed.  It  is  not  possible  to  close 
handsomely  the  two  pieces  at  once.  The  tube  is  seldom  perfectly 
finished  by  the  operation  ;  a  superfluous  knob  of  glass  generally 
remains  upon  the  end.  If  small,  it  may  be  got  rid  of  by  heating  the 
whole  end  of  the  tube,  and  blowing  moderately  with  the  mouth  into 
the  open  end.  The  knob  being  hotter,  and  therefore  softer  than  any 
other  part,  yields  to  the  pressure  from  within,  spreads  out  and  disap- 
pears. If  the  knob  is  large,  it  may  be  drawn  off  by  sticking  to  it  a 
fragment  of  tube,  and  then  softening  the  glass  above  the  junction. 
The  same  process  may  be  applied  to  the  too  pointed  end  of  the  right- 
hand  half  of  the  original  tube,  or  to  any  misshapen  result  of  an  unsuc- 
cessful attempt  to  close  a  tube,  or  to  any  bit  of  tube  which  is  too  short 
to  make  two  closed  tubes.  When  the  closed  end  of  a  tube  is  too  thin, 
it  may  be  strengthened  by  keeping  the  whole  end  tit  a  red  heat  for  two 
or  three  minutes,  turning  the  tube  constantly  between  the  fingers.  It 
may  be  said  in  general  of  all  the  preceding  operations  before  the 
lamp,  that  success  depends  on  keeping  the  tube  to  be  heated  in  constant 
25* 


Vi  APPENDIX. 

rotation,  in  order  to  secure  a  uniform  temperature  on  all  sides  of  the 
tube. 

4.  Blowing  Bulbs  and  Piercing  Holes  in  Tubing.  —  If  the 
bulb  desired  is  large  in  proportion  to  the  size  of  the  tube  on  which 
it  is  to  be  made,  the  walls  of  the  tube  must  be  thickened  by  rotation 
in  the  flame  of  the  Bunsen  burner,  or  of  the  blast-lamp,  before  the 
bulb  can  be  blown.  If  the  bulb  is  to  be  blown  in  the  middle  of  a 
piece  of  tubing,  this  thickening  is  effected  by  gently  pressing  the 
ends  of  the  tube  together  while  the  glass  is  red-hot  in  the  place 
where  the  bulb  is  to  be  ;  if  the  bulb  is  to  be  placed  at  the  end  of  a 
tube,  this  end  is  first  closed,  and  then  suitably  thickened  by  keeping 
the  closed  end  of  the  tube  in  the  flame,  and  turning  it  continually, 
until  enough  has  been  accumulated  at  the  end.*  The  glass  is  then 
suddenly  withdrawn  from  the  flame,  and  the  thickened  portion  ex- 
panded while  hot  by  steadily  blowing,  or  rather  pressing,  air  into  the 
tube  with  the  mouth  ;  the  tube  must  be  constantly  turned  on  its  axis, 
not  only  while  in  the  flame,  but  also  while  the  bulb  is  being  blown. 
If  too  strong  or  too  sudden  a  pressure  be  exerted  with  the  mouth,  the 
bulb  will  be  extremely  thin  and  quite  useless.  By  watching  the  ex- 
panding glass,  the  proper  moment  for  arresting  the  pressure  may 
usually  be  determined.  If  the  bulb  obtained  be  not  large  enough,  it 
may  be  reheated  and  enlarged  by  blowing  into  it  again,  provided  that 
a  sufficient  thickness  of  glass  remain. 

It  is  sometimes  necessary  to  make  a  hole  in  the  side  of  a  tube  or 
other  thin  glass  apparatus.  This  may  be  done  by  directing  a  pointed 
flame  from  the  blast-lamp  upon  the  place  where  the  hole  is  to  be,  until 
a  small  spot  is  red-hot,  and  then  blowing  forcibly  into  one  end  of  the 
tube  while  the  other  end  is  closed  by  the  finger  ;  at  the  hot  spot  the 
glass  is  blown  out  into  a  thin  bubble,  which  bursts,  or  may  be  easily 
broken  off,  leaving  an  aperture  in  the  side  of  the  tube. 

Era.  v.  It  is  hoped  that  these  few  directions  will  enable  the 

Q  attentive   student  to  perform,  sufficiently  well,  all  the 

manipulations  with  glass  tubes  which  ordinary  chemical 
experiments  require.  Much  practice  will  alone  give  a 
perfect  mastery  of  the  details  of  glass-blowing. 

5.  Lamps.  —  The  common  glass  spirit-lamp  will  be 
understood  without  description  from  the  figure  (Fig. 
V).  This  lamp  does  not  give  heat  enough  for  most 
ignitions  ;  for  such  purposes  a  lamp  with  circular  wick,  of  some  one 
of  the  numerous  forms  sold  under  the  name  of  Berzelius's  Argand 


APPENDIX. 


vn 


FIG.  VI. 


Spirit-Lamp  (Fig.  VI),  is  necessary.  These  argand  lamps  are 
usually  mounted  on  a  lamp-stand  provided  with  three  brass  rings," 
but  the  fittings  of  these  lamps 
are  all  made  slender,  in  order 
not  to  carry  off  too  much 
heat.  When  it  is  necessary  to 
heat  heavy  vessels,  other  sup- 
ports must  be  used. 

Whenever  gas  can  be  ob- 
tained, gas-lamps  are  greatly 
to  be  preferred  to  the  best 
spirit-lamps.  For  all  ordinary 
experiments,  except  those  for 
which  ignition-tubes  must  be 
prepared,  or  in  which  con- 
siderable lengths  of  tubing 
must  be  heated,  the  gas-lamp 
known  as  Bunsen's  burner  will  be  sufficient.  Fig.  VII  represents  a 
cheap  and  excellent  form  of  the  Bunsen  lamp.  The  single  casting  of 
brass  a  b  comprises  the  tube  b  through  which  the  gas  enters,  and  the 
block  a  from  which  the  gas  escapes  by  FIG.  vn. 

two  or  three  fine  vertical  holes  passing 
through  the  screw  d,  and  issuing  from 
the  upper  face  of  d,  as  shown  at  e. 
The  length  of  the  tube  b  is  4.5  c.  m., 
and  its  outside  diameter  varies  from 
0.5  c.  m.  at  the  outer  end  to  1  c.  m.  at 
the  junction  with  the  block  a.  The 
outside  diameter  of  the  block  a  is 
1.6  c.  m.,  and  its  outside  height  with- 
out the  screws  is  1.8  c.  m.  By  the 
screw  c,  the  piece  a  b  is  attached  to  the  iron  foot  #,  which  may  be  6  c.  m. 
in  diameter.  By  the  screw  d.  the  brass  tube  /  is  attached  to  the  cast- 
ing a  6.  The  diameter  of  the  face  e,  and  therefore  the  internal  diameter 
of  the  tube  /  should  be  8  m.  m.  The  length  of  the  tube  /  is  9  c.  m. 
Through  the  wall  of  this  tube,  four  holes  5  m.  m.  in  diameter  are  to 
be  cut  at  such  a  height  that  the  bottom  of  each  hole  will  come  1  m.  m. 
above  the  face  e  when  the  tube  is  screwed  upon  a  b.  These  holes  are 
of  course  opposite  each  other  in  pairs.  The  finished  lamp  is  also 
shown  in  Fig.  VII.  To  the  tube  b  a  caoutchouc  tube  of  5  to 


Vlll 


APPENDIX. 


FIG.  VIII. 


7  m.  m.  internal  diameter  is  attached  ;  this  flexible  tube  should  be 
about  1  m.  long,  and  its  other  extremity  should  be  connected  with 
the  gas-cock  through  the  intervention  of  a  short  piece  of  brass  gas- 
pipe  screwed  into  the  cock.  In  cases  where  a  very  small  flame  is  re- 
quired, as,  for  instance,  in  evaporating  small  quantities  of  liquid,  a 
piece  of  wire  gauze,  somewhat  larger^  than  the  opening  of  the  tube  / 
should  be  laid  across  the  top  of  the  tube,  and  its  projecting  edges 
pressed  down  tightly  against  the  sides  of  the  tube  before  the  gas  is- 
lighted.  In  default  of  this  precaution,  the  flame  of  a  Bunsen  burner, 
when  small,  and  exposed  to  currents  of  air,  is  liable  to  pass  down  the 
tube  and  ignite  the  gas  at  d. 

A  smaller  and  somewhat  cheaper  lamp,  made  on  the  same  principle 
as  the  ordinary  Bunsen,  burner,  is  represented  in  Fig.  VIII.  The 
"  tip  "  of  the  burner  is  cast  of  brass,  and  the 
construction  will  be  evident  from  the  en- 
larged section  (6).  The  stand  or  foot  is  the 
same  as  shown  in  Fig.  VII,  except  that 
the  opening  for  the  gas  is  larger.  These 
lamps  are  excellent  where  a  small  flame  is 
required,  as  it  is  almost  impossible  for  the 
gas  to  "  back  down  "  and  ignite  at  the  lower 
opening.  Tips  are  also  made,  as  shown  at  c, 
the  upper  opening  being  closed,  and  the  gas  issuing  from  smaller 
openings  in  the  sides  of  the  tube  forms  a  "rose"  ;  this  form  of  burner 
is  of  especial  service  when  evaporating  a  solution  in  a  porcelain  dish 
where  it  is  desirable  to  heat  the  liquid  equably.  Either  of  the  tips 
described  may  be  screwed  upon  an  ordinary  gas-burner  in  default  of 
the  stand  or  foot  above  represented. 

A  lamp  to  give  a  powerful  flame  8  or  10  c.  m. 
long,  suitable  for  heating  tubes,  may  be  very 
simply  constructed  by  boring  two  holes,  entering 
the  side  and  issuing  at  the  upper  face,  through  a 
block  of  compact  hard  wood,  10  c.  m.  by  6.5  c.  m. 
by  3.5  c.  m.,  and  fitting  short  pieces  of  brass  tub- 
ing into  the  holes  so  formed.  To  the  tubes  at  the 
side  are  attached  the ,  caoutchouc  tubes  which  de- 
liver the  gas,  and  from  the  tubes  at  the  top  the 
gas  issues  under  a  sheet-iron  funnel  closed  at  the  top  with  wire-gauze. 
Above  this  gauze,  the  mixture  of  gas  and  air  is  to  be  lighted.  The 


FIG.  IX. 


APPENDIX. 


IX 


FIG.  X. 


iron  funnel  will  be  readily  understood  from  Fig.  IX,  and  the  follow- 
ing dimensions  ;  length  of  the  wire-gauze,  10  c.  m  ;  width  of  the  gauze 
5  c.  m.  ;  width  at  a  b,  9  c.  m.  ;  height  of  the  line  a  b  from  the  table, 
8.5  c.  m.  ;  whole  height  of  the  funnel,  21  c.  m.  A  partition  parallel 
to  a  b  divides  the  funnel  into  two  equal  parts  from 
the  gauze  to  the  level  of  a  b.  A  long  flame  may  also 
be  produced  with  a  Bunse.n  burner,  which  may  con- 
veniently be  somewhat  larger  than  the  one  described 
on  the  preceding  page,  and  which  is  provided  with  a 
copper  or  brass  attachment  as  represented  in  Fig. 
X.  This  attachment  slips  over  the  top  of  the  tube, 
/(  see  Fig.  VII)  ;  the  flame  is  of  the  same  character 
as  that  ordinarily  produced,  but  of  a  different  shape. 
Two  of  these  lamps  side  by  side  will  heat  a  sufficient 
length  of  glass  or  iron  tube  for  all  ordinary  experi- 
ments. 

6.  Blast-lamps  and  Blowers.  —  For  drawing,  bending  and 
closing  large  glass  tubes,  a  blast- 
lamp  is  necessary.  The  best  form  is 
that  sold  under  the  name  of  Bunsen's 
Gas  Blowpipe.  Its  construction  and 
the  method  of  using  it  may  be  learned 
from  Fig.  XI  ;  a  bis  the  pipe  through 
which  the  gas  enters,  c  is  the  tube 
for  the  blast  of  air ;  the  relation  of 
the  air-tube  to  the  external  gas-tube 
is  shown  at  d  ;  there  is  an  outer  slid- 
ing tube  by  which  the  form  and 
volume  of  the  flame  can  be  regu- 
lated. 

If  gas  is  not  to  be  had,  a  lamp 
burning  oil  or  naphtha  must  be  em- 
ployed.    Fig.  XII  represents  a  glass-blower's  lamp  made  of  tin  and 
suitable  for  burning  oil.     A  large  wick 
is   essential,  whether  oil  or  naphtha  be 
the  combustible. 

For  every  blast-lamp  a  blowing- 
machine  of  some  sort  is  necessary. 
To  supply  a  constant  blast  it  is  essen- 
tial that  the  bellows  be  of  that 


FIG.  XII. 


APPENDIX. 


construction  called  double.     Fig.  XIII  represents  a  very  good  form 
of  blowpipe-table,  made  by  J.  H.  Call,  North  Billerica,  Mass.,  and 


FIG.  xni. 


costing  about  thirty  dollars.  The  bellows  are  made  of  seamless  rub- 
ber cloth  ;  the  table  is  0.8  metre  high,  from  which  the  other  dimen- 
sions may  be  inferred.  A  simpler  form  of  bellows,  and  one  which 


FIG  XIV. 


can  be  made  by  any  carpenter  or  cabinet-maker,  is  represented  in 
perspective  and  in  section  on  Fig.  XIV.  The  sides  of  the  bellows 
and  of  the  reservoir  are  made  of  stout  leather.  The  arrangement  of 
valves  will  be  evident  from  the  figure  ;  a  constant  pressure  is  main- 
tained on  the  reservoir  by  means  of  a  spiral  spring,  and  the  air  is 
delivered  through  the  tube  t.  The  rod  which  is  represented  in  the 
figure  serves  simply  as  a  guide.  The  entire  length  from  a  to  b  may  be 
0.6  metre. 

7.   Blowpipes.  — -  The  mouth-blowpipe  in  its  simplest  form  is  a 


APPENDIX. 


tube  bent  near  one  extremity  at  a  right  angle.  Fig.  XV,  a,  repre- 
sents a  common  form  of  blowpipe  used  by  jewellers.  The  blowpipe 
is  rendered  more  convenient  by  the  addition  of  a  mouth-piece  and 
a  chamber  near  the  right  angle  for  the  con-  FIG.  xv. 

densation  of  moisture.  Fig.  XV,  b  and  c, 
represent  different  forms  of  blowpipe  thus  fur- 
nished. The  cheapest  and  best  form  of  mouth 
blowpipe  for  chemical  purposes  is  a  tube  of 
tin-plate,  about  18  c.  m.  long,  2  c.  m.  broad  at 
one  end,  and  tapering  to  0.7  c.  m.  at  the  other 
(Fig.  XV,  b)  ;  the  broad  end  is  closed,  and 
serves  to  retain  the  moisture  ;  a  little  above 
this  closed  end  a  small  cylindrical  tube  of 
'brass  about  5  c.  m.  long  is  soldered  in  at  right 
angles  ;  this  brass  tube  is  slightly  conical  at  the  end,  and  carries  a 
small  nozzle  or  tip,  which  may  be  made  either  of  brass  or  platinum. 
The  tip  should  be  drilled  out  of  a  solid  piece  of  metal,  and  should 
not  be  fastened  upon  the  brass  tube  with  a  screw.  A  trumpet-shaped 
mouth-piece  of  horn  or  boxwood  is  a  convenient,  though  by  no  means 
essential,  addition  to  this  blowpipe.  For  convenience  in  cleaning  and 
packing,  blowpipes  are  often  made  in  several  pieces,  as  is  the  one 
represented  in  Fig.  XV,  c. 

The  blowpipe  may  be  used  with  a  candle,  with  gas  or  with  any 
hand-lamp  proper  for  burning  oil,  petroleum  or  any  of  the  so-called 
burning  fluids,  provided  that  the  form  of  the  lamp  below  the  wick- 
holder  is  such  as  to  permit  the  close  approach  of  the  object  to  be 
heated  to  the  side  of  the  wick.  When  a  lamp  is  used,  a  wick  about 
1.2  c.  m.  long  and  0.5  c.  m.  broad  is  more  convenient  than  a  round  or 
narrow  wick.  The  wick-holder  should  be  filed  off  on  its  longer 
dimension  a  little  obliquely,  and  the  wick  cut  parallel  to  the  holder, 
in  order  that  the  blowpipe  flame  may  be  directed  downwards  when 
necessary  (Figs.  47,  48,  page  130).  A  gas  flame  suitable  for  the  blow- 
pipe is  readily  obtained  by  slipping  a  narrow  brass  tube  (i\  open  at 
both  ends,  into  the  tube  /  of  Bunsen's  burner.  (See  Fig.  VII.) 
This  blowpipe-tube  must  be  long  enough  to  close  the  air  apertures  in 
the  tube/,  and  should  be  pinched  together  and  filed  off  obliquely  on 
top  ;  it  may  usually  be  obtained  with  the  burner  from  dealers  in 
chemical  ware. 

8.  Caoutchouc.  —  Vulcanized  caoutchouc  is  a  most  useful  sub- 
stance in  the  laboratory,  on  account  of  its  elasticity,  and  because  it 


xii  APPENDIX. 

resists  so  well  most  of  the  corrosive  substances  with  which  the  chemist 
deals.  It  is  used  in  tubing  of  various  diameters  comparable  with  the 
sizes  of  glass  tubing,  and  in  stoppers  of  various  sizes  to  replace  corks. 
Caoutchouc  tubing  may  be  used  to  conduct  all  gases  and  liquids  which 
do  not  corrode  its  substance,  provided  that  the  pressure  under  which 
the  gas  or  liquid  flows  be  not  greater,  or  their  temperature  higher, 
than  the  texture  of  the  tubing  can  endure.  The  flexibility  of  the 
tubing  is  a  very  obvious  advantage  in  a  great  variety  of  cases.  Short 
pieces  of  such  tubing,  a  few  centimetres  in  length,  are  much  used, 
under  the  name  of  connectors,  to  make  flexible  joints  in  apparatus,  of 
which  glass  tubing  forms  part ;  flexible  joints  add  greatly  to  the  dura- 
bility of  such  apparatus,  because  long  glass  tubes  bent  at  several 
angles  and  connected  with  heavy  objects,  like  globes,  bottles  or  flasks 
full  of  liquid,  are  almost  certain  to  break  even  with  the  most  careful 
usage  ;  gas-delivery  tubes,  and  all  considerable  lengths  of  glass  tubing, 
should  invariably  be  divided  at  one  or  more  places,  and  the  pieces 
joined  again  with  caoutchouc  connectors.  The  ends  of  glass  tubing 
to  be  thus  connected  should  be  squarely  cut,  and  then  rounded  in  the 
lamp,  in  order  that  no  sharp  edges  may  cut  the  caoutchouc  ;  the  in- 
ternal diameter  of  the  caoutchouc  tube  must  be  a  little  smaller  than 
the  external  diameter  of  the  glass  tubes  ;  the  slipping  on  of  the  con- 
nector is  facilitated  by  wetting  the  glass. 

Caoutchouc  stoppers  of  good  quality  are  much  more  durable  than 
corks,  and  are  in  every  respect  to  be  preferred.  The  German  stop- 
pers are  of  excellent  shape  and  quality  ;  the  American,  being  chiefly 
intended  for  wine-bottles,  are  apt  to  be  too  conical.  Caoutchouc 
stoppers  can  be  bored,  like  corks  (see  the  next  section),  by  means  of 
suitable  cutters,  and  glass  tubes  can  be  fitted  into  the  holes  thus  made 
with  a  tightness  unattainable  with  corks.  German  stoppers  may  be 
bought  already  provided  with  one,  two  and  three  holes.  It  is  not 
well  to  lay  in  a  large  stock  of  caoutchouc  stoppers,  for,  though  they 
last  a  long  time  when  in  constant  use,  they  not  infrequently  deteri- 
orate when  kept  in  store,  becoming  hard  and  somewhat  brittle  with 
age. 

9.  Corks.  —  It  is  often  very  difficult  to  obtain  sound,  elastic  corks 
of  fine  grain  and  of  size  suitable  for  large  flasks  ^nd  wide-mouthed 
bottles.  On  this  account,  bottles  with  mouths  not  too  large  to  be 
closed  with  a  cork  cut  across  the  grain  should  be  chosen  for  chemical 
uses,  in  preference  to  bottles  which  require  large  corks  or  bungs  cut 
with  the  grain,  and  therefore  offering  continuous  channels  for  the 


APPENDIX. 


Xlll 


FIG.  XVI. 


passage  of  gases,  or  even  liquids.  The  kinds  sold  as  champagne 
corks  and  as  satin  corks  for  phials  are  suitable  for  chemical  use.  The 
best  corks  generally  need  to  be  softened  before  using  ;  this  softening 
may  be  effected  by  rolling  the  cork  under  a  board  upon  the  table,  or 
under  the  foot  upon  the  clean  floor,  or  by  gently  squeezing  it  on  all 
sides  with  the  well-known  tool  expressly  adapted  for  this  purpose,  and 
thence  called  a  cork-squeezer.  Steaming  also  softens  the  hardest 
corks. 

Corks  must  often  be  cut  with  cleanness  and  precision  ;  a  sharp,  thin 
knife,  such  as  shoemakers  use,  is  desirable  for  this  purpose.  When  a 
cork  has  been  pared  down  to  reduce  its  diameter,  a  flat  file  may  be 
employed  in  finishing  ;  the  file  must  be  fine  enough  to  leave  a  smooth 
surface  upon  the  cork  ;  in  tiling  a  cork,  a  cylindrical,  not  a  conical 
form  should  be  aimed  at. 

In  boring  holes  through  corks  to  receive  glass  tubes,  a  hollow 
cylinder  of  sheet  brass  sharpened  at  one  end  is  a  very  convenient 
tool.  Fig.  XVI.  represents  a  set  of  such 
little  cylinders  of  graduated  sizes,  slipping  one 
within  the  other  into  a  very  compact  form  ;  a 
stout  wire,  of  the  same  length  as  the  cylinders, 
accompanies  the  set,  and  serves  a  double  pur- 
pose,—  passed  transversely  through  two  holes 
in  the  cap  which  terminates  each  cylinder,  it 
gives  the  hand  a  better  grasp  of  the  tool  while 
penetrating  the  cork  ;  and  when  the  hole  is 
made,  the  wire  thrust  through  an  opening  in  the 
top  of  the  cap  expels  the  little  cylinder  of  cork, 
which  else  would  remain  in  the  cutting  cylinder 
of  brass.  That  cutter  whose  diameter  is  next 
below  that  of  the  glass  tube  to  be  inserted  in 
the  cork  is  always  to  be  selected,  and  if  the  hole  it  makes  is  too  small, 
a  round  file  must  be  used  to  enlarge  the  aperture. 

Cutters  which  have  been  dulled  by  use  may  be  sharpened  by  filing 
or  grinding  down  their  outer  bevelled  edges,  and  then  paring  off  with 
a  sharp  penknife  any  protuberance  or  roughness  which  may  remain 
upon  the  inside  of  the  edge. 

A  flask  which  presents  sharp  or  rough  edges  at  the  mouth  can 

seldom  be  tightly  corked,  for  the  cork  cannot  be  introduced  into  the 

neck  without  being  cut  or  roughened  ;    such  sharp  edges  must  be 

rounded  in  the  lamp.     In  thrusting  glass  tubes  through  bored  corks, 

26 


xiv  APPENDIX. 

the  following  directions  are  to  be  observed  :  (1.)  The  end  of  the  tube 
must  not  present  a  sharp  edge  capable  of  cutting  the  cork.  (2.)  The 
tube  should  be  grasped  very  close  to  the  cork,  in  order  to  escape 
cutting  the  hand  which  holds  the  cork,  should  the  tube  break  ;  by 
observing  this  precaution  the  chief  cause  of  breakage,  viz.,  irregular 
lateral  pressure,  will  be  at  the  same  time  avoided.  (3.)  A  funnel- 
tube  must  never  be  held  by  the  funnel  in  driving  it  through  a  cork, 
nor  a  bent  tube  grasped  at  the  bend,  unless  the  bend  comes  immedi- 
ately above  the  cork.  (4.)  If  the  tube  goes  very  hard  through  the 
cork,  the  application  of  a  little  soap  and  water  will  facilitate  its  pas- 
sage, but  if  soap  is  used  the  tube  can  seldom  be  withdrawn  from  the 
cork  after  the  latter  has  become  dry.  (5.)  The  tube  must  not  be 
pushed  straight  into  the  cork,  but  screwed  in,  as  it  were,  with  a  slow 
rotary  as  well  as  onward  motion.  Joints  made  with  corks  should 
always  be  tested  before  the  apparatus  is  used  by  blowing  into  the 
apparatus  and  at  the  same  time  stopping  up  all  legitimate  outlets. 
Any  leakage  is  revealed  by  the  disappearance  of  the  pressure  created. 
To  the  same  end,  air  may  be  sucked  out  of  an  apparatus  and  its  tight- 
ness proved  by  the  permanence  of  the  partial  vacuum.  To  attempt 
to  use  a  leaky  cork  is  generally  to  waste  time  and  labor  and  to  insure 
the  failure  of  the  experiment. 

10.  Iron-stand,  Sand-bath  and  Wire-gauze.  —  To  support 
vessels  over  the  gas-lamp,  an  iron  stand  is  used  consisting  of  a 
FIG.  xvn.  stout  vertical  rod  fastened  into  a  heavy,  cast-iron  foot, 
and  two  or  more  iron  rings  of  graduated  sizes  secured 
to  the  vertical  rod  with  binding  screws  ;  all  the  rings 
may  be  slipped  off  the  rod,  or  any  ring  may  be  adjusted 
at  any  convenient  elevation.  As  a  general  rule,  it  is 
not  best  to  apply  the  direct  flame  of  the  lamp  to  glass 
and  porcelain  vessels  ;  hence  a  piece  of  wire-gauze  is 
stretched  loosely  over  the  largest  ring,  and  bent  down- 
wards a  little  for  the  reception  of  round-bottomed 
vessels  ;  on  this  gauze,  flasks,  retorts  and  porcelain 
dishes  are  usually  supported.  In  a  few  cases,  in  which 
a  very  gradual  and  equable  heat  is  required,  the  wire- 
gauze  is  replaced  by  a  small,  shallow  pan,  beaten  out  of  sheet-iron, 
and  filled  with  dry  sand.  This  arrangement  is  called  a  sand-bath. 
With  the  aid  of  annealed  iron  wire,  the  iron-stand  may  be  made 
available  for  supporting  tubes  over  the  lamp.  Crucibles,  or  dishes, 
too  small  for  the  smallest  ring  belonging  to  the  stand,  are  con- 


APPENDIX.  XV 

venieixtly  supported  on  an  equilateral  triangle  made  of  three  pieces 

of  soft  iron  wire  twisted  together  at  the  apices  ;  this  triangle  is  laid  on 

one  of  the  rings  of  the  stand.     An  iron  tripod  —          FIG.  xvm. 

that  is,  a  stout  ring  supported  on  three  legs  —  may 

often  be  used  instead  of  the  stand  above  described, 

but  it  is  not  so  generally  useful  because  of  the 

difficulty  of  adjusting  it  at  various  heights  ;  with  a 

sufficiency  of  wooden  blocks  wherewith  to  raise 

the  lamp  or  the  tripod  as  occasion  may  require,  , 

it  may  be  made  available. 

11.  Pneumatic  Trough.  —  The  pneumatic  trough  is  a  contri- 
vance which  enables  us  to  collect  and  confine  gases  in  suitable  vessels, 
and  to  decant  them  from  one  vessel  to  another.  Its  efficiency  depends 
on  the  pressure  of  the  atmosphere,  which  as  we  know  is  capable  of 
supporting  a  column  of  water  10.33  metres  long  or  a  column  of  mer- 
cury 76  c.  m.  long,  provided  that  the  liquid  column  be  so  arranged  that 
the  atmospheric  pressure  shall  be  fully  felt  upon  the  foot  of  the  column, 
but  not  at  all  upon  its  head.  If  a  tube,  closed  at  one  end  and  open 
at  the  other,  and  of  any  length  less  than  10.33  m.,  be  completely  filled 
with  water,  and  then  inverted  so  that  its  open  end  shall  dip  beneath 
some  water  held  in  a  basin  or  saucer,  the  tube  will  remain  full  .of 
water  when  the  thumb  or  cork,  which  closed  the  open  end  while  the 
inversion  was  effected,  is  withdrawn.  What  is  true  of  a  tube  is 
equally  true  of  a  bell,  or  other  vessel  closed  at  one  end,  of  any  diame- 
ter or  shape,  provided  its  height  be  not  greater  than  10.33  m.  ;  and 
the  principle  which  applies  to  water  is  equally  applicable  to  mercury, 
except  that  the  height  of  the  mercury  column,  which  the  average 
atmospheric  pressure  can  hold  up,  is  only  76  c.  m.,  because  mercury 
is  13.596  times  heavier  than  water.  If  a  few  bubbles  of  any  gas 
insoluble  in  water  should  be  delivered  beneath  the  open  end  of  a 
tube  thus  standing  full  of  water  in  apparent  defiance  of  gravitation, 
the  gas  would  rise  to  the  top  of  the  tube,  by  virtue  of  being  lighter  than 
the  water,  and  the  exact  volume  of  water  displaced  by  the  gas,  small 
or  large,  would  drop  into  the  basin  or  saucer,  beneath.  If  the  gas  were 
thus  delivered  continuously  beneath  the  tube  or  bell,  we  should  finally 
get  the  tube  full  of  gas,  without  admixture  of  air,  and  sealed  at  the 
bottom  by  the  water  in  the  basin  or  saucer.  If  mercury  were  the 
liquid,  the  operation  would  be  precisely  the  same,  except  as  regards 
the  height  of  the  tube.  Even  this  difference  of  possible  height  is  not 
noticeable  in  practice,  because  bell-glasses  and  bottles  more  than 


xvi  APPENDIX. 

50  c.  m.  high  are  very  seldom  used  with  either  liquid.  On  account  of 
its  costliness,  mercury  is  rarely  used,  unless  the  gas  to  be  collected, 
or  experimented  upon,  be  soluble  in  water.  A  trough  for  mercury  is 
made  as  small  as  possible  for  the  same  reason.  It  is  obvious  that  the 
object  of  a  pneumatic  trough  may  be  accomplished  under  a  great 
variety  of  forms.  Any  bucket,  or  tub,  with  a  hanging  shelf  in  it,  may 
be  made  to  serve.  It  will  be  sufficient  to  describe  two  convenient 
forms  of  the  apparatus. 

A  cheap  pneumatic  trough  is  represented  in  Fig.  XIX.     It  con- 
FIG.  xix.  sists  of  two  pieces,  1st,  a  stone-ware  pan, 

about  30  c.  m.  in  diameter  on  the  bot- 
tom, with  sides  sloping  slightly  outwards 
and  rising  to  the  height  of  about  10  c.  m.  ; 
2d,  a  deep  flower-pot  saucer  about  15  c.  m. 
in  diameter,  with  one  hole  bored  through 
the  middle  of  the  bottom,  and  a  second 
arched  hole  nipped  out  of  its  rim  ;  this  saucer  is  inverted  in  the 
pan.  If  this  second  piece  be  made  expressly  for  this  purpose,  it 
should  be  made  abo;it  5  c.  m.  high,  and  its  interior  should  be  rounded 
to  the  hole  in  the  centre,  while  the  outside  is  left  flat,  like  the  flower- 
pot saucer.  Two  blocks  of  wood  of  equal  thickness,  loaded  with  lead, 
or  two  small  blocks  of  stone,  may  be  used  instead  of  the  saucer  ;  the 
delivery-tube  rests  between  them,  and  the  bottle  or  gas-cylinder  is 
supported  directly  over  the  mouth  of  the  delivery-tube.  To  use  this 
apparatus,  the  pan  is  filled  with  water  to  a  level  about  2  c.  m.  above 
the  top  of  the  inverted  saucer  ;  the  bottle,  cylinder  or  bell  which  is 
to  receive  the  gas  is  completely  filled  with  water  from  a  pitcher  or 
water-cock,  then  closed  with  the  hand  of  the  operator,  or  with  a  flat 
piece  of  glass  or  wood,  inverted  into  the  pan,  and  placed  on  the 
saucer  over  the  hole  in  its  centre  ;  the  end  of  the  gas-delivery-tube  is 
thrust  through  the  side  hole  in  the  saucer,  and  the  gas  rising  through 
the  centre  hole  bubbles  up  into  the  bottle  or  cylinder  placed  to  receive 
it.  While  one  bottle  is  filling  with  gas,  another  is  made  ready  to 
replace  it,  and  when  the  first  is  full,  it  is  pushed  off  the  centre  hole 
of  the  saucer,  and  the  second  bottle  is  brought  over  the  hole.  A 
bottle  full  of  gas  may  be  removed  from  the  trough  by  slipping  beneath 
the  mouth  of  the  bottle  a  shallow  plate  or  dish,  and  then  lifting  plate 
and  bottle  out  of  the  pan  together  in  such  a  manner  that  water 
enough  to  seal  the  mouth  of  the  bottle  shall  remain  in  the  plate.  The 
gas  in  one  bottle  may  be  decanted  upwards  into  another,  by  filling 


APPENDIX. 


XVll 


the  second  bottle  with  water,  and  then  carefully  inclining  the  bottle 
containing  the  gas  so  as  to  bring  its  mouth  under  the  mouth  of  the 
bottle  which  is  full  of  water,  keeping  the  mouths  of  both  bottles  all 
the  time  beneath  the  surface  of  the  water  in  the  pan.  If  the  gas 
which  has  been  collected  is  heavier  than  air,  a  bottle  of  it  may  be 
withdrawn  from  the  water-pan  and  got  at  for  use,  by  simply  slipping 
a  flat  piece  of  glass  or  wood  beneath  its  mouth  so  as  to  close  it  rather 
tightly,  and  then  standing  the  bottle,  mouth  upward,  upon  the  table. 
If  the  cover  be  then  removed  from  the  bottle,  the  gas  will  not  flow 
out,  though  it  will  slowly  diffuse  into  the  air.  As  the  water  with  which 
the  bottles  or  cylinders  are  filled  falls  into  the  pan  when  displaced  by 
gas,  it  is  possible  that  the  pan  may  become  inconveniently  full  if  many 
large  bottles  are  used  ;  this  difficulty  must  be  remedied  by  dipping 
water  out  of  the  pan,  and  so  restoring  the  true  level. 

Where  considerable  quantities  of  gas  are  frequently  to  be  handled, 
and  large  vessels  are  therefore  necessary,  the  apparatus  shown  in 
Fig.  XX  is  much  more  convenient  FIG.  XX. 

than  the  small  pan,  which  suffices 
for  all  common  experiments.  The 
form  of  this  larger  pneumatic 
trough,  and  the  mode  of  using  it, 
will  readily  be  understood  from 
the  figure  ;  the  depth  and  width 
of  the  tank  or  well  must  be  deter- 
mined by  the  size  of  the  bells 
and  cylinders  which  are  to  be 
sunk  in  it,  and  the  length  and  breadth  of  the  shallow  part  or  shelf 
by  the  number  of  bells  or  jars  of  gas  which  are  likely  to  be  in  use  at 
any  one  time.  The  deep  groove  in  the  shelf  permits  a  glass  or 
caoutchouc  tube  to  pass  without  compression  under  a  bell  whose  rim 
projects  over  the  groove.  Such  a  trough  is  best  made  of  wood  lined 
with  lead  ;  zinc  may  be  used  for  the  lining  where  no  acids  are  likely 
to  be  present.  It  is  very  convenient  to  have  it  sunk  in  a  table,  and 
permanently  provided  with  a  water-cock  and  drain-pipe.  A  chief 
merit  of  this  instrument  is  that  the  glass  vessels  used  can  be  filled 
with  water  by  sinking  them  in  the  well  much  more  conveniently 
than  from  a  pitcher  or  water-cock. 

A  pneumatic  trough  for  mercury  may  be  made  either  of  wood,  iron 
or  stone.     For  all  common  uses,  it  is  very  well  cut  out  of  a  solid  block 
of  compact  hard  wood,  which  will  not  split.     Small  cylinders  or  bells 
26* 


xviii  APPENDIX. 

only  can  be  used,  and  the  well  of  the  trough  should  be  scooped  out 
but  a  little  larger  than  the  bell  or  cylinder  selected,  with  its  princi- 
pal dimension  horizontal,  and  its  bottom  curved  to  fit  the  cylindrical 
bell  which  is  to  be  laid  in  it ;  the  shelf,  too,  should  have  but  a  small 
area,  sufficient  only  for  four  or  five  bells  of  3  or  4  c.  m.  diameter. 

In  using  a  pneumatic  trough,  of  any  construction  or  dimensions, 
the  student  should  be  on  his  guard  against  two  difficulties  of  possible 
occurrence,  —  against  the  sucking  back  of  the  liquid  in  the  trough  into 
the  gas-generating  apparatus,  and  against  the  leakage  sometimes  in- 
duced by  the  pressure  created  by  thrusting  the  gas-delivery-tube  deep 
under  water  or  mercury.  The  first  of  these-  difficulties  is  the  most 
serious.  When  the  flow  of  gas  from  a  heated  flask  or  tube  is  suddenly 
arrested,  in  consequence  of  some  reduction  of  temperature,  or  from 
any  other  cause,  it  often  happens  that  the  volume  of  gas  in  the  gen- 
erating apparatus  contracts,  and  the  cold  water  or  mercury  from  the 
trough  rises  in  the  delivery-tube  to  fill  the  void  ;  if  the  contraction  is 
so  considerable  as  to  suffer  the  cold  liquid  to  penetrate  into  the  hot 
flask  or  tube,  an  explosion  almost  inevitably  ensues,  which  fractures 
the  apparatus,  if  it  does  no  worse  damage  In  collecting  over  water 
a  gas  somewhat  soluble  in  that  liquid,  this  danger  is  especially  immi- 
nent. The  occurrence  of  such  accidents  may  be  effectually  guarded 
against  by  paying  attention  to  the  following  directions  :  (1.)  When- 
ever it  is  proposed  to  stop  an  evolution  of  gas  which  has  been  going 
on  from  a  hot  flask  or  tube,  withdraw  the  delivery-tube  from  the 
water  before  extinguishing  the  lamp,  and  shake  off  from  the  bent  end 
of  the  tube  the  drops  of  water  which  are  apt  to  adhere  to  it  ;  the  lamp 
may  then  be  safely  put  out,  for  air  can  enter  the  apparatus  through 
the  open  tube.  (2.)  When  the  flow  of  gas  from  a  hot  apparatus  is 
observed  to  slacken,  watch  closely  the  escape  of  the  gas  from  the 
delivery-tube,  and  as  soon  as  any  tendency  to  reflux  of  water  is 
detected,  lift  the  delivery-tube  quickly  out  of  the  water,  or,  better,  slip 
off  the  caoutchouc  connector,  which  should  always  be  found  between 
the  flask  and  the  water-pan  on  every  such  piece  of  apparatus  ;  if  there 
be  no  connector,  the  cork  must  be  loosened  in  the  neck  of  the  flask. 
Air  will  thus  be  admitted  to  the  hot  flask  or  tube. 

These  precautions  apply  more  particularly  to  the  cases  where  gas 
is  evolved  from  dry  materials,  as  in  making  oxygen  or  nitrous  oxide  ; 
when  a  liquid  is  contained  in  the  generating  flask,  a  safety-tube  (see 
Fig.  20)  is  a  sure  protection  against  the  danger  of  sucking  back. 
The  atmospheric  pressure  can  force  air  into  a  flask,  in  which  a  partial 


APPENDIX. 


xix 


vacuum  has  been  created,  through  the  safety-tube,  by  lifting  and  dis- 
placing a  column  of  the  liquid  whose  height  is  the  length  of  that 
portion  of  the  safety-tube  which  dips  beneath  the  liquid.  Unless  the 
liquid  in  the  flask  be  extraordinarily  dense,  the  force  required  to  do 
this  will  be  very  much  less  than  that  required  to  lift  a  column  of  water 
whose  height  is  determined  by  the  elevation  of  the  highest  point  of 
the  delivery-tube  above  the  level  of  the  water  in  the  pan. 

When  the  gas  coming  from  the  generating  flask  has  to  force  out 
and  keep  out  of  the  delivery-tube  a  column  of  water  measured  from 
the  lowest  point  of  the  tube  to  the  surface  of  the  water  in  the  pan,  a 
pressure  determined  by  the  height  of  this  column  is  established  upon 
the  interior  of  the  flask  and  upon  every  joint  of  the  apparatus.  Hence 
an  apparatus  will  sometimes  leak,  and  refuse  to  deliver  gas  at  the  de- 
sired point,  when  its  delivery-tube  is  deeply  immersed,  while  it  does 
not  leak  if  the  tube  merely  dip  beneath  the  surface  of  the  water.  With 
mercury  the  pressure  of  a  few  centimetres  is  very  considerable,  on 
account  of  the  high  specific  gravity  FlG-  XXL 

of  the  fluid,  so  that  this  difficulty  is 
more  likely  to  occur  with  this  metal 
than  with  water.  Tight  joints  pre- 
vent the  occurrence  of  this  difficulty. 
A  partial  remedy  is  to  dip  the  de- 
livery-tube as  little  as  possible  below 
the  surface  of  the  fluid  in  the  trough. 

12.  Gas-holders.  —  A  small  gas- 
holder, very  convenient  for  many 
uses,  is  made  from  a  common  glass 
bottle  in  the  following  manner  :  A 
(Fig.  XXI)  is  a  bottle  of  4  to  6 
litres'  capacity  ;  through  the  cork  in 
its  neck  pass  two  glass  tubes  (No.  6), 
of  which  one  reaches  the  bottom  of 
the  bottle,  while  the  other  merely 
penetrates  the  cork  ;  with  the  outer 
end  of  the  first  tube  a  caoutchouc 
tube  c  is  connected,  with  the  outer 
end  of  the  second  a  common  gas- 
cock  a.  The  bottle  being  first  completely  filled  with  water,  the  ap- 
paratus which  generates,  or  contains  the  gas  to  be  introduced  into  the 
holder  is  connected  with  the  tube  carrying  the  cock  a ;  this  cock  is 


W , 


XX 


APPENDIX. 


FIG.  XXII. 


open.  As  the  gas  presses  in,  the  water  mounts  in  the  long  tube,  and 
flows  out  by  the  siphon  c.  In  order  to  relieve  the  gas  from  this  pres- 
sure at  the  beginning,  it  is  only  necessary  to  suck  a  little  at  c.  The 
tube  c  should  of  course  be  thrust  into  a  sink  or  drain-pipe. 

To  get  gas  out  of  the  bottle,  thus  charged,  the  cock  a  is  closed,  and 
the  flexible  tube  c  is  lifted  up  and  connected,  as  shown  in  the  figure, 
with  a  bottle  of  water  B  placed  on  a  shelf,  or  stand,  somewhat  above 
the  bottle  A.  When  the  cock  6  is  opened,  the  gas  in  A  is  pressed 
upon  by  the  weight  of  the  superincumbent  column  of  water,  and  may 
therefore  be  made  to  issue  at  will  from  the  cock  a.  The  higher  B  is 
placed  above  A,  the  greater  will  be  the  force  with  which  the  gas  will 
issue.  If  a  moderate,  or  easily  regulated  water-pressure  is  at  hand, 
supplied  by  city  water-works  or  a  reservoir  in  the  upper  part  of  the 
building,  the  bottle  B  is  unnecessary,  and  the  flexible  tube  c  may  be 
connected  with  such  a  water-supply,  whenever  gas  is  to  be  pressed 
out  of  the  gas-holder,  A. 

When  larger  quantities  of  gas  are  to  be  stored  for  use,  a  metallic 
gas-holder,  whose  construction  and  propor- 
tions are  shown  in  Fig.  XXII,  is  advan- 
tageously employed.  The  open  cistern  B 
is  supported  over  the  vessel  A  on  two  col- 
ums  c,  c,  and  two  tubes  a  and  6  ;  of  these 
tubes,  the  first,  a,  reaches  from  the  bottom 
of  B  nearly  to  the  bottom  of  A,  while  the 
second,  6,  starts  from  the  bottom  of  B  and 
just  enters  the  arched  top  of  A  without 
projecting  into  it  ;  d  is  a  short,  large  tube, 
sloping  upwards  and  outwards,  and  capable 
of  being  tightly  closed  with  a  cork  or  caout- 
chouc stopper  ;  g  is  a  glass  gauge  to  show 
the  height  of  the  water  in  the  vessel  A  ; 
e  is  the  discharge-pipe.  To  fill  the  gas- 
holder with  water,  close  d,  open  the  stop- 
cocks a,  &,  and  e,  and  pour  water  into  the 
cistern  B  ;  the  water  entering  A  will  expel 
the  air  through  6  and  e  ;  when  the  water 
begins  to  flow  through  e,  close  that  stop-cock  and  expel  the  rest  of  the 
air  through  6.  The  gas-holder  may  now  be  filled  with  gas  by  displa- 
cing the  water  in  the  following  manner  :  —  Close  all  the  stop-cocks, 
withdraw  the  cork  or  stopper  from  d,  and  introduce  the  tube  which 


APPENDIX.  xxi 

delivers  the  gas  through  that  opening  ;  a  short  piece  of  caoutchouc 
tubing  makes  the  best  end  for  the  gas- delivery-tube,  but  glass  tubing 
will  answer  the  purpose  if  the  end  be  slightly  bent  upward  ;  the  water 
Hows  out  at  d  as  fast  as  the  gas  enters,  and  the  gas-holder  should 
therefore  stand  in  a  shallow  metal  tray  provided  with  a  drain-pipe. 
When  the  desired  quantity  of  gas  has  been  introduced,  close  d.  To 
draw  gas  out  of  a  gas-holder  of  this  construction,  the  cistern  B  is 
filled  with  water  and  the  cork  a  is  opened  ;  under  the  pressure  thus 
established  the  gas  may  be  drawn  off  through  e,  or  allowed  to  rise 
through  b  into  bottles  or  bells  filled  with  water  and  held  over  the 
mouth  of  the  tube  b  in  the  cistern  B ;  in  this  last  case  B  answers  the 
purpose  of  a  pneumatic  trough. 

This  gas-holder  may  be  cheaply  made  of  zinc  ;  any  gas-fitter  can 
supply  the  necessary  stop-cocks  ;  care  must  be  taken  that  the  glass 
tube  which  constitutes  the  gauge  is  fitted  air-tight  to  the  gas-holder. 
The  stop-cock  e  need  not  end  in  a  screw  ;  tubes  may  be  as  well  con- 
nected with  it  by  caoutchouc.  The  available  pressure,  under  which  the 
gas  in  the  holder  streams  out  at  e,  is  of  course  limited  by  the  elevation 
of  B  above  A,  which  must  always  be  moderate.  When  a  stronger 
pressure  is  desirable,  as  in  getting  the  oxy-hydrogen  blowpipe  flame, 
for  example,  a  heavier  water-column  may  be  obtained  by  screwing  a 
tall  tube  with  a  capacious  funnel  on  top  of  it  into  the  tube  a,  where  it 
opens  into  the  bottom  of  the  cistern  B.  A  piece  of  common  iron  or 
copper  gas-pipe,  about  a  metre  long,  answers  this  purpose  very  well  ; 
the  funnel  at  the  top  should  hold  two  or  three  litres,  and  must  be  kept 
full  of  water  from  a  cask  or  tub  provided  with  a  cork  and  placed  just 
above  the  funnel.  Where  a  water-supply,  with  moderate  pressure,  is 
obtainable,  it  may  be  used  to  keep  the  funnel  full,  or  to  replace  the 
funnel  altogether,  if  directly  connected  with  the  tube  a.  A  gas- 
holder, measuring  not  more  than  50  c.  m.  in  total  height,  is  not  too 
heavy  to  be  portable,  and  during  the  process  of  filling  may  be  placed 
over  a  tub  ;  but  a  gas-holder  of  much  larger  proportions  is  better 
made  a  fixture,  and  provided  in  a  permanent  manner  with  drain-pipe 
and  water-supply.  The  gas-holder  thus  described  is  that  which  is  the 
most  generally  useful ;  it  may  be  charged  from  any  glass  flask,  retort 
or  bottle,  without  any  pressure  being  exerted  upon  the  glass  vessel  ; 
and  unused  gas  contained  in  any  sort  of  bell,  bottle,  or  flask,  can  be 
very  readily  transferred  to  such  a  gas-holder  without  waste  and  with 
very  little  trouble. 

A  cheaper  gas-holder  may  be  made  on  the  plan  of  the  large  gas- 


XXIV 


APPENDIX. 


FIG.  XXV. 


FIG.  xxiv.  and  one  thickness  upon  the  other,  as  shown  in  the 
upper  half  of  Fig.  XXIV  ;  the  filter  is  then  placed 
in  a  glass  funnel,  the  angle  of  which  should  be  pre- 
cisely that  of  the  opened  paper,  viz.,  60°.  The 
paper  may  be  so  folded  as  to  fit  a  funnel  whose 
angle  is  more  or  less  than  60°,  but  this  is  the 
most  advantageous  angle,  and  funnels  should  be 
selected  with  reference  to  their  correctness  in  this 
respect. 

.  In  the  second  method  of  folding  filters,  the  circle  of  paper  is 
doubled  once  upon  itself  as  before  into  the  form  of  a  semicircle,  and 
a  fold  equal  to  one  quarter  of  this  semicircle  is  turned  down  on  each 
side  of  the  paper.  Each  of  the  quarter  semicircles  is  then  folded 
back  upon  itself,  as  shown  in  the  lower  half  of  Fig. 
XXV  ;  the  filter  is  opened,  without  disturbing  the 
folded  portions,  and  placed  in  the  funnel.  Filtration- 
can  be  rapidly  effected  with  this  kind  of  filter,  for 
the  projecting  folds  keep  open  passages  between  the 
filter  and  the  funnel,  and  thus  facilitate  the  passage 
of  the  liquid.  That  portion  of  the  circle  of  paper 
which  must  necessarily  be  folded  up  in  order  to  give 
the  requisite  conical  form  to  a  paper  filter  retards 
filtration  in  the  first  manner  of  folding,  but  helps  it  in  the  second. 

Coarse  and  rapid  fil-     FIG.  xxvii. 
tering  can  be  effected 
with  cloth  bags  ;  also 
by  plugging  the  neck 
of    a    funnel    loosely 
with  tow  or  cotton.     If 
a    very   acid   or  very 
caustic   liquid,   which 
would    destroy  paper, 
cotton,    tow   or   wool, 
is    to    be    filtered,  th 
best   substances   wherewith  to   plug 
the  neck  of  the  funnel  are  asbestos 
and  gun-cotton,  neither  of  which  is 
attacked  by  such  corrosive  liquids. 
The  glass  funnel  which  holds  the  filter  generally  requires  an  inde- 
pendent support,  for  it  is  seldom  judicious,  or  possible,  to  support 


FIG.  XXVI. 


APPENDIX. 


XXV 


the  funnel  directly  upon  the  vessel  which  receives  the  filtrate,  as  the 
clear  liquid  which  runs  through  the  filter  is  called.  The  iron  stand 
(Fig.  XVII)  may  be  used  for  this  purpose  ;  and  wooden  stands,  of 
the  form  represented  in  Fig.  XXVI,  adapted  expressly  for  holding 
funnels,  are  very  convenient  and  not  expensive.  In  general,  care 
should  be  taken  that  the  lower  end  of  the  funnel  touch  the  side  or 
edge  of  the  vessel  into  which  the  filtrate  descends,  in  order  that  the 
liquid  may  not  fall  in  drops,  but  run  quietly  down  without  splashing. 
Sometimes  there  is  no  objection  to  thrusting  a  funnel  directly  into  the 
neck  of  a  bottle  or  flask,  but  in  this  case  an  ample  exit  for  the  air 
in  the  bottle  must  be  provided  (Fig.  XXVII). 

16.  Drying  Gases.  —  It  is  often  desirable  to  remove  the  aqueous 
vapor  which  is  mixed  with  gases  collected  over  water,  or  prepared 
from  materials  containing  water.  It  very  seldom  happens  that  a  gas 
can  be  prepared  at  one  operation  in  so  dry  a  state  as  to  contain  no 
vapor  of  water  ;  this  vapor  must  ordinarily  be  removed  by  a  subse- 
quent or  additional  process.  Experience  has  shown  that  some  gases 
are  more  easily  dried  than  others  ;  thus  air,  hydrogen  and  common 
oxygen  are  thoroughly  dried  with  great  ease,  but  gases  which  contain 
antozone  only  with  great  difficulty  ;  chlorine  is  three  times  as  hard  to 
dry  as  carbonic  acid.  These  and  similar  facts  must  be  borne  in  mind 
in  constructing  drying  apparatus.  The  common  drying  process  de- 
pends upon  bringing  the  moist  gas  into  contact  with  some  liquid  or 
solid  which  greedily  and  rapidly  absorbs  aqueous  vapor.  The  three 
substances  most  used  for  this  purpose  are  concentrated  sulphuric  acid, 
calcium  chloride  and  dry  quicklime.  Sulphuric  acid  may  be  used 
in  two  ways  :  the  gas  may  be  made 
to  bubble  through  a  few  centi- 
metres' depth  of  the  liquid  acid, 
or  it  may  be  forced  to  pass  through 
the  interstices  of  a  column  of  bro- 
ken pumice-stone  which  has  been 
previously  soaked  in  the  acid.  The 
latter  method  is  the  most  effectual, 
because  it  secures  a  more  thorough 
contact  of  the  gas  with  the  hygro- 
scopic acid  than  is  possible  during  =&? —  — Q^ 
the  rapid  bubbling  of  the  light  gas 
through  a  shallow  layer  of  the  dense 

liquid.     The  column  of  fragments  of  pumice-stone  may  be  held  in  a 
27 


FIG.  XXVIII. 


APPENDIX. 

U-tube,  arranged  like  that  shown  in  Fig.  XXVIII  ;  but  the  vertical 
cylinder  shown  in  the  same  figure  is  better  adapted  for  this  use,  be- 
cause the  acid,  as  it  becomes  dilute  from  absorption  of  moisture,  grad- 
ually trickles  from  the  pumice-stone,  and  is  apt  to  collect  in  such  quan- 
tity at  the  bottom  of  the  U-tube  as  to  completely  close  the  tube.  In 
preparing  the  upright  cylinder  for  use,  the  portion  below  the  contrac- 
tion is  not  filled  with  pumice-stone  ;  it  receives  the  drippings  from  the 
pumice-stone  column.  The  gas  to  be  dried  enters  by  the  lower  lateral 
opening,  and  goes  out  at  the  top  of  the  cylinder.  Though  especially 
adapted  to  the  column  of  acid-soaked  pumice-stone,  this  cylinder  may 
very  well  be  used  with  either  of  the  other  drying  agents,  calcium, 
chloride  or  quicklime.  Either  of  the  forms  of  drying-tube  represented 
in  Fig.  XXVIII  may  be  employed  with  these  latter  substances  ;  in 
charging  the  horizontal  tubes,  bits  of  loose  cotton- wool  should  first  be 
placed  against  the  exit-tube  to  prevent  any  particles  of  the  calcium 
chloride,  or  quicklime,  from  entering  that  tube  ;  pieces  of  the 
perfectly  dry  solid  are  then  introduced  in  such  a  way  that  the  tube 
may  be  compactly  filled  with  fragments  which  leave  room  for  the  gas 
to  pass  very  deviously  between  them,  but  offer  no  direct  channels 
through  which  the  gas  could  find  straight  and  quick  passage.  Quick- 
lime must  be  charged  much  more  loosely  than  calcium  chloride, 
because  of  its  great  expansion  when  moistened.  Fused  calcium 
chloride  is  not  so  well  adapted  for  drying  gases  as  the  unfused  sub- 
stance. It  is  not  at  all  necessary  that  the  fragments  of  calcium 
chloride,  or  quicklime,  should  be  of  uniform  size.  When  the  tube  is 
nearly  full,  a  plug  of  loose  cotton  should  be  inserted  before  putting 
in  the  cork.  A  calcium  chloride  tube,  once  filled,  will  often  serve 
for  many  experiments  ;  whenever  out  of  use,  its  outlets  should  be 
covered  with  paper  caps  ;  or,  better,  caoutchouc  connectors  may  be 
slipped  upon  the  exit-tubes,  and  bits  of  glass  rod  thrust  into  these 
connectors.  The  moisture  of  the  air  is  thus  kept  from  the  calcium 
chloride.  The  dimensions  of  drying-tubes  are  of  course  very  va- 
rious ;  the  bulb-tube  shown  in  Fig.  XXVIII  is  seldom  used  with  a 
greater  length  than  25  c.  m.  ;  when  this  form  of  tube  is  employed  the 
gas  should  invariably  enter  by  the  end  without  a  cork,  where  the 
small  size  of  the  tube  permits  direct  connection  with  a  common  gas- 
delivery-tube  by  means  of  a  caoutchouc  connector  ;  the  other  hori- 
zontal tube,  shown  in  the  figure,  may  be  of  any  length,  but  whenever 
a  great  extent  of  drying  surface  is  necessary,  U-tubes  have  the  advan- 
tage of  compactness,  for  many  can  be  hung  upon  one  short  frame  ; 
the  upright  cylinder  may  be  from  25  c.  m.  to  40  c.  m.  in  height. 


APPENDIX.  xxvij 

The  choice  between  one  or  other  of  the  three  drying  substances  is 
determined  in  each  special  case  by  the  chemical  relations  of  the  gas 
to  be  dried  ;  thus  ammonia-gas,  which  is  absorbed  by  sulphuric  acid 
and  by  calcium  chloride,  must  be  dried  by  passing  it  over  quick- 
lime, while  sulphurous  acid  gas,  which  would  combine  with  quick- 
lime, must  be  dried  by  contact  with  sulphuric  acid. 

17.  Water-bath.  —  It  is  often  necessary  to  evaporate  solutions 
at  a  moderate  temperature  which  can  permanently  be  kept  below  a 
certain  known  limit  ;  thus,  when  an  aqueous  solution  is  to  be  quietly 
evaporated  without  spirting  or  jumping,  the  temperature  of  the  solu- 
tion must  never  be  suffered  to  rise  above  the  boil-  FIG.  xxix. 
ing-point  of  water,  nor  even  quite  to  reach  this 
point.  This  quiet  evaporation  is  best  effected  by 
the  use  of  a  water-bath,  —  a  copper  cup  whose 
top  is  made  of  concentric  rings  of  different  di- 
ameters to  adapt  it  to  dishes  of  various  sizes  (Fig. 
XXIX).  This  cup,  two-thirds  full  of  water,  is 
supported  on  the  iron-stand  over  the  lamp,  and 
the  dish  containing  the  solution  to  be  evaporated  is  placed  on  that 
one  of  the  several  rings  which  will  permit  the  greater  part  of  the  dish 
to  sink  into  the  copper  cup.  The  steam  rising  from  the  water  im- 
pinges upon  the  bottom  of  the  dish,  and  brings  the  liquid  within  it  to 
a  temperature  which  insures  the  evaporation  of  the  water,  but  will  not 
cause  any  actual  ebullition.  The  water  in  the  copper  cup  must  never 
be  allowed  to  boil  away.  Wherever  a  constant  supply  of  steam  is  at 
hand,  as  in  buildings  warmed  by  steam,  the  copper  cup  above  described 
may  be  converted  into  a  steam-bath  by  attaching  it  to  a  steam-pipe  by 
means  of  a  small  tube  provided  with  a  stop-cock. 

A  cheap  but  serviceable  water-bath  may  be  made  from  a  quart 
milk-can,  oil-can,  tea-canister,  or  any  similarly  shaped  tin  vessel,  by 
inserting  the  stem  of  a  glass  funnel  into  the  neck  of  the  can  through  a 
well-fitting  cork.  In  this  funnel  the  dish  containing  the  liquor  to  be 
evaporated  rests.  The  can  contains  the  water,  which  is  to  be  kept 
just  boiling.  On  account  of  the  shape  of  the  funnel,  dishes  of  various 
sizes  can  be  used  with  the  same  apparatus. 

When  a  gradual  and  equable  heat  higher  than  can  be  obtained 
upon  the  water-bath  is  required,  a  sand-bath  will  sometimes  be  found 
useful.  A  cheap  and  convenient  sand-bath  may  be  made  by  beating 
a  disk  of  thin  sheet-iron,  about  four  inches  in  diameter,  into  the  form 
of  a  saucer  or  shallow  pan,  and  placing  within  it  a  quantity  of  dry 


XXV111 


APPENDIX. 


FIG.  XXX. 


sand.    The  dish  or  flask  to  be  heated  is  embedded  in  the  sand,  and  the 
apparatus  placed  upon  a  ring  of  the  iron-stand  over  a  gas-lamp. 

18.  Self-regulating  Gas-generator.  —  An  apparatus  which  is 
always  ready  to  deliver  a  constant,  stream  of  hydrogen,  and  yet  does 
not  generate  the  gas,  except  when  it  is  immediately  wanted  for  use, 
is  a  great  convenience  in  an  active  laboratory  or  on  a  lecture-table. 
The  same  remark  applies  to  the  two  gases,  hydrogen  sulphide  and 
carbonic  acid,  which  are  likewise  used  in  considerable  quantities, 
and  which  can  be  conveniently  generated 
in  precisely  the  same  form  of  apparatus 
which  is  advantageous  for  hydrogen.  Such 
a  generator  may  be  made  of  divers  dimen- 
sions. The  following  directions,  with  the 
accompanying  figure  (Fig.  XXX),  will 
enable  the  student  to  construct  an  ap- 
paratus of  convenient  size.  Procure  a 
glass  cylinder  20  or  25  c.  m.  in  diam- 
eter and  30  or  35  c.  m.  high  ;  ribbed 
candy-jars  are  sometimes  to  be  had  of 
about  this  size  ;  procure  also  a  stout  tubu- 
lated bell-glass  10  or  12  c.  m.  wide  and 
5  or  7  c.  m.  shorter  than  the  cylinder.  Get 
a  basket  of  sheet-lead  7.5  c.  m.  deep  and 
2.5  c.  m.  narrower  than  the  bell-glass,  and 
bore  a  number  of  small  holes  in  the  sides  and  bottom  of  this  basket. 
Cast  a  circular  plate  of  lead  7  m.  m.  thick  and  of  a  diameter  4  c.  m. 
larger  than  that  of  the  glass  cylinder  ;  on  what  is  intended  for  its 
under  side  solder  three  equidistant  leaden  strips,  or  a  continuous  ring 
of  lead,  to  keep  the  plate  in  proper  position  as  a  cover  for  the  cylin- 
der. Fit  tightly  to  each  end  of  a  good  brass  gas-cock  a  piece  of  brass 
tube  8  c.  m.  long,  1.5  to  2  c.  m.  wide,  and  stout  in  metal.  Perforate 
the  centre  of  the  leaden  plate,  so  that  one  of  these  tubes  will  snugly 
pass  through  the  orifice,  and  secure  it  by  solder,  leaving  5  c.  m.  of  the 
tube  projecting  below  the  plate.  Attach  to  the  lower  end  of  this  tube 
a  stout  hook  on  which  to  hang  the  leaden  basket.  By  means  of  a 
sound  cork  and  common  sealing-wax,  or  a  cement  made  of  oil  mixed 
with  red  and  white  lead,  fasten  this  tube  into  the  tubulure  of  the 
bell-glass  air-tight,  and  so  firmly  that  the  joint  will  bear  a  weight  of 
several  pounds.  Hang  the  basket  by  means  of  copper  wire  within  the 
bell  5  c.  m.  above  the  bottom  of  the  latter.  To  the  tube  which  extends 


APPENDIX.  xxix 

above  the  siop-cock  attach  by  a  good  cork  the  neck  of  a  tubulated 
receiver  of  100  or  150  c.  c.  capacity,  the  interior  of  which  has  been 
loosely  stuffed  with  cotton.  Into  the  second  tubulure  of  the  receiver 
fit  tightly  the  delivery-tube  carrying  a  caoutchouc  connector  ;  into 
this  connector  can  be  fitted  a  tube  adapted  to  convey  the  gas  in  any 
desired  direction.  This  apparatus  is  charged  by  placing  the  zinc, 
iron  sulphide  or  marble,  as  the  case  may  be,  in  the  basket,  hanging 
the  basket  in  the  bell,  and  then  putting  the  bell-glass  full  of  air  into 
its  place  and  closing  the  stop-cock ;  the  cylinder  is  then  filled  with 
dilute  acid  to  within  4  c.  m.  of  the  top.  On  opening  the  cock,  the 
weight  of  the  acid  expels  the  air  from  the  bell,  the  acid  comes  in  con- 
tact with  the  solid  in  the  basket,  and  a  steady  supply  of  gas  is  gener- 
ated until  either  the  acid  is  saturated  or  the  solid  dissolved  :  if  the 
cock  be  closed,  the  gas  accumulates  in  the  bell,  and  pushes  the  acid 
below  the  basket,  so  that  all  action  ceases.  In  cold  weather  the  ap- 
paratus must  be  kept  in  a  warm  place.  For  generating  hydrogen, 
sulphuric  acid  diluted  with  four  or  five  parts  of  water  is  used  ;  for 
hydrogen  sulphide,  sulphuric  acid  is  diluted  with  fourteen  parts  of 
water  ;  for  carbonic  acid,  chlorhydric  acid  diluted  with  two  or  three 
parts  of  water  is  to  be  preferred. 

19.  Glass  Retorts,  Flasks,  Beakers,  Test-tubes,  Test- 
glasses  and  Bottles.  —  All  glass  vessels  which  are  meant  for  use 
in  heating  liquids  must  have  uniformly  thin  bottoms.  Tubulated  re- 
torts are  much  more  generally  useful  than  those  without  a  tubulure  ; 
as  retorts  are  expensive  in  comparison  with  flasks,  they  are  less  used 
than  formerly. 

The  neck  of  a  flask  should  have  such  a  form  that  it  can  be  tightly 
closed  by  a  cork,  and  the  lip  must  be  strengthened  to  resist  the  force 
used  in  pressing  in  the  cork,  either  by  a  rim  of  glass  added  on  the 
outside,  or  better  by  causing  the  rim  itself  to  flare  outward.  The 
actual  edge  of  the  rim  must  never  be  sharp  or  rough,  but  always 
smooth  and  rounded  by  partial  fusion. 

Beakers  are  thin  flat-bottomed  tumblers  with  a  slightly  flaring  rim. 
They  are  to  be  bought  in  sets  or  nests  which  sometimes  include  a 
large  range  of  sizes.  The  small  sizes  are  very  useful  vessels ;  the 
large  are  so  fragile  as  to  be  almost  worthless.  Up  to  the  capacity  of 
about  a  litre,  beakers  are  to  be  recommended  for  heating  liquids 
whenever  it  is  an  object  to  have  the  whole  interior  of  the  vessel 
readily  accessible. 

Test-tubes  are  little  cylinders  of  thin  glass,  with  round,  thin  b,ot- 


XXX  APPENDIX. 

toms,  and  lips  slightly  flared.     Their  length  may  be  from  12  c.  m.  to 
18  c.  m.,  and  their  diameter  1  c.  m.  to  2  c.  m.  ;  they  should  never  have 
FIG.  xxxi.  a  diameter  so  large  that   the    open    end 

cannot  be  closed  by  the  ball  of  the  thumb. 
To  hold  the  tubes  upright  a  wooden  rack 
is  necessary  ;  besides  the  row  of  holes  to 
receive  a  dozen  test-tubes  bottom  down, 
the  rack  should  have  a  row  of  pegs  on 
which  the  test-tubes  may  be  inverted 
when  not  in  use  ;  in  this  position  the 
water  in  which  they  are  rinsed  drains  off, 
and  dust  cannot  be  deposited  within  the  tubes.  Test-tubes  are  much 
used  for  heating  small  quantities  of  liquid  over  the  gas-  or  spirit-lamp  ; 
they  may  generally  be  held  by  the  upper  end  in  the  fingers  without 
inconvenience,  but  if  a  liquid  is  to  be  boiled  long  in  a  test-tube,  the 
tube  must  be  held  in  wooden  nippers  (see  Fig.  1),  or  in  a  strip  of  thick 
folded  paper,  nipped  round  the  tube  and  grasped  between  the  thumb 
and  forefinger  just  outside  the  tube.  The  wooden  nippers,  above 
mentioned,  are  made  of  two  bits  of  wood  about  a  foot  long  hinged  to- 
gether at  the  back,  and  at  once  connected  and  kept  apart  by  a  sliding 
steel  or  brass  spring,  somewhat  like  those  used  on  certain  pruning- 
shears  and  some  kinds  of  steel  nippers.  When  a  liquid  is  boiling 
actively  in  a  test-tube,  it  sometimes  happens  that  portions  of  the  hot 
liquid  are  projected  out  of  the  tube  with  some  force  ;  the  operator 
should  always  be  careful  not  to  direct  a  tube,  which  he  is  thus  using, 
either  towards  himself  or  towards  any  other  person  in  his  neighbor- 
hood. Test-tubes  are  cleaned  by  the  aid  of  cylindrical  brushes,  made 
of  bristles  caught  between  twisted  wires,  like  those  used  for  cleaning 
lamp-chimneys  :  they  should  have  a  round  end  of  bristles. 

An  excellent  holder  (see  Fig.  35),  devised  by  Professor  Caldwell, 
is  made  of  flexible  copper  or  brass  wire,  1%  m.m.  thick.  This  wire  is 
twisted  about  a  cork  which  serves  as  a  handle,  or,  being  perforated, 
the  cork  may  be  slipped  on  to  the  rod  of  a  ring-stand.  By  opening 
the  coils  at  the  ends  more  or  less,  it  can  be  adapted  to  any  test-tube  or 
ignition  tube,  and  the  tube  can  be  supported  at  any  angle. 

Two  precautions  are  invariably  to  be  observed  in  heating  test-tubes  ; 
first,  the  outside  of  the  tube  must  be  wiped  perfectly  dry  ;  secondly, 
the  tube  must  be  moved  in  and  out  of  the  flame  for  a  minute  or  two 
when  first  heated.  It  should  be  rolled  to  and  fro  also  to  a  slight 
extent  between  the  thumb  and  forefinger,  in  order  that  each  side  of  it 


APPENDIX.  xxxi 

may  be  equally  exposed  to  the  flante.  A  drop  of  water  on  the  out- 
side of  the  tube  keeps  one  spot  cooler  than  the  rest.  The  tube 
breaks,  because  its  parts,  being  unequally  heated,  expand  unequally, 
and  tear  apart. 

In  heating  glass  and  porcelain  vessels  of 'whatever  form,  the  tem- 
perature must  not  be  raised  too  rapidly.  When  a  large  flask  or 
beaker  containing  a  cold  liquid  is  first  warmed  over  a  lamp,  moisture 
almost  invariably  condenses  upon  the  bottom  of  the  vessel  :  this 
moisture  should  be  wiped  off  with  a  cloth. 

Stout  conical  glasses  with  strong  stems  and  feet  are  convenient  for 
many  uses  not  involving  the  application  of  heat.  They  are  called 
test-glasses,  and  may  be  had  of  various  shapes  and  sizes.  It  is 
obvious  that  cheap  wine-  or  beer-glasses  and  common  jelly-tumblers 
would  answer  the  purposes  which  these  test-glasses  serve. 

For  the  collection  of  gases  at  the  pneumatic  trough,  and  for  many 
other  purposes,  ordinary  green  glass  "  packing-bottles  "  may  take  the 
place  of  more  expensive  apparatus.  The  smaller  sizes  may  be  con- 
veniently used  instead  of  beakers  and  test-glasses,  but  the  bottles  can- 
not be  used  for  the  heating  of  liquids. 

20.  Pipettes.  —  Pipettes  are  tubes  drawn  to  a  point  and  some- 
times furnished  with  a  bulb  or  a  cylindrical  enlargement.     They  are 
chiefly  used  to  suck  small  quantities  of  fluid  out  of  a    FlQ  xxxn 
vessel  without  disturbing  the  bulk  of  the  liquid.     Fig. 

XXXII  represents  three  forms  of  pipette  ;  the  form  with 
the  lower  end  bent  upwards  is  used  to  introduce  liquids 
into  a  bell  or  bottle  of  gas  standing  over  mercury. 
Pipettes  graduated  into  cubic  centimetres,  or  holding  a 
certain  number  of  cubic  centimetres  when  filled  to  a 
mark  on  the  stem,  are  often  convenient. 

Measuring-glasses,  divided  into  cubic  centimetres,  are 
made  in  the  cylindrical  form  and  also  in  the  flaring 
shape  common  in  druggists'  measuring-glasses  ;  the  cylindrical  form 
is  to  be  preferred.  Such  a  glass  of  250  c.  c.,  or  better  of  500  c.  c. 
capacity,  is  a  very  useful  implement :  flasks  holding  1  litre,  500  c.  c.,, 
or  250  c.  c.,  when  filled  to  a  mark  on  the  neck,  are  also  conve- 
nient. 

21.  Porcelain   Dishes   and   Crucibles.  —  Open  dishes,  which 
will  bear  heat  without  cracking,  are  necessary  implements  in   the 
laboratory  for  conducting  the  evaporation  of  liquids.     The  best  evap- 
orating-dishes  are  those  made  of  Berlin  porcelain,  glazed  both  inside 


xxxii  APPfitfDIX. 

and  out,  and  provided  with  a  little  lip  projecting  beyond  the  rim. 
The  dishes  made  of  Meissen  porcelain  are  not  glazed  on  the  outside, 
and  are  not  so  durable  as  those  of  Berlin  manufacture  ;  but  they  are 
much  cheaper,  and  with  proper  care  last  a  long  time.  The  small 
Berlin  dishes  will  generally  bear  an  evaporation  to  dryness  on  the 
wire-gauze  over  the  open  flame  of  the  gas-lamp  ;  the  Meissen  dishes 
do  not  so  well  endure  this  severe  treatment.  Evaporating-dishes  are 
made  of  all  diameters  from  3  c.  m.  to  45  c.  m.  ;  they  should  be 
ordered  by  specifying  the  diameter  desired.  The  large  sizes  are 
expensive,  and  not  very  durable  ;  they  should  never  be  used  except 
on  a  sand-bath.  Dishes  of  German  earthenware  are  as  good  as  porce- 
lain for  many  uses,  and  are  much  to  be  recommended  in  place  of  the 
xxxni  large  sizes  of  porcelain  dishes. 

Deep    porcelain  dishes    provided    with    handles 
(called  casseroles)  are  very  useful  in  heating  liquids 
which  have  a  tendency  to  froth  (see  Exps.  Ill  and 
113),  and  may  be  obtained  of  various  sizes. 

Very  thin,  highly  glazed  porcelain  crucibles  with  glazed  covers 
are  made  both  at  Berlin  and  at  Meissen,  near  Dresden  ;  they  are 
indispensable  implements  to  the  chemist.  In  general,  the  Meissen 
crucibles  are  thinner  than  the  Berlin,  but  the  Berlin  crucibles  are 
somewhat  less  liable  to  crack  ;  both  kinds  are  glazed  inside  and  out, 
except  on  the  outside  of  the  bottom.  Crucibles  should  be  ordered  by 
specifying  the  diameters  of  the  sizes  desired  ;  they  are  to  be  had  of 
nearly  a  dozen  different  sizes,  with  diameters  varying  from  2  c.  m.  to 
9  c.  m.  The  smallest  and  largest  sizes  are  little  used  ;  for  most 
purposes  the  best  sizes  are  those  between  3  c.  m.  and  5  c.  m.  in 
diameter.  As  the  covers  are  much  less  liable  to  be  broken  than  the 
crucibles,  it  is  advantageous  to  buy  more  crucibles  than  covers,  when- 
ever it  is  possible  so  to  do.  Porcelain  crucibles  are  supported  over 
the  lamp  on  an  iron- wire  triangle  ;  they  must  always  be  gradually 
heated,  and  never  brought  suddenly  in  contact  with  any  cold  substance 
while  they  are  hot. 

22.  Rings  to  Support  round-bottomed  Vessels.  —  It  is 
often  necessary  to  support  globes,  round-bottomed  flasks,  evaporating- 
dishes,  and  round  receivers  in  a  stable  manner  upon  the  table  or  other 
flat  surface.  For  this  purpose  rings  are  used,  made  of  braided  straw, 
or  of  straw  wound  about  a  core  of  straw,  or  of  tin  wound  with  list- 
ing or  coarse  woollen  cloth.  The  material  of  which  these  rings  are 
made,  or  with  which  they  are  covered,  ought  to  be  a  substance  which 


APPENDIX.  xxxiii 

does  not  conduct  heat  well,  because  one  of  the  chief  uses  of  these  rings 
is  to  receive  hot  vessels  just  removed  from  the  lamp  or  sand-bath.  A 
hot  flask  or  dish  would  almost  certainly  be  broken,  if  it  were  placed 
upon  the  cold  surface  of  a  good  conductor  of  heat.  The  student 
must  never  touch  a  hot  vessel  with  cold  water,  or  bring  it  into  sudden 
contact  with  a  surface  of  marble,  iron,  copper,  or  other  good  conductor 
of  heat. 

23.  Crucibles,  Furnaces,  Tongs  and  Iron  Retort.  —  For 
preparing  granulated  zinc  on  a  considerable  scale  and  for  other  pur- 
poses, the  cheapest  crucibles,  and  those  which  are  most  used,  are  those 
known  as  Hessian  crucibles.  These  Hessian  crucibles  are  sold  in 
nests  containing  from  3  to  10  crucibles  ;  there  are  10  sizes,  which 
vary  from  3  to  25  c.  in.-  in  height.  They  generally  have  a  triangular 
form,  and  will  withstand  a  very  high  temperature,  if  they  are  warmed 
before  being  put  in  the  fire.  They  are  not  sold  with  covers  ;  but 
covers  may  be  bought  separately,  or  a  triangular  piece  of  soapstone 
may  be  very  conveniently  used  as  a  cover.  Crucibles  are  mainly 
used  for  the  fusion  and  reduction  of  metals,  but  there  are  also  many 
chemical  compounds  which  can  only  be  prepared  at  the  very  high 
temperatures  which  by  the  use  of  crucibles  we  are  able  to  command. 
Although  crucibles  often  withstand  the  most  sudden  changes  of 
temperature,  it  is,  nevertheless,  expedient  as  a  general  rule  to  heat  up 
a  crucible  gradually,  and  to  previously  warm  a  charge  which  is  to  be 
placed  in  a  crucible  already  hot.  If  a  cold  crucible  is  to  be  intro- 
duced into  a  fire,  it  should  first  be  placed  in  the  coldest  part  of  the 
fire  and  gradually  brought  into  the  hottest  part. 

For  heating  these  crucibles  an  anthracite  or  coke  fire  in  an  ordinary 
cylinder  stove  will  in  most  cases  suffice.  The  chafing-dish  or  open 
portable  stove,  such  as  is  used  by  plumbers,  for  example,  is  very  con- 
venient for  operations  which  require  less  heat.  The  clay  buckets  used 
as  open  furnaces  are  better  than  the  iron  6nes,  because  they  hold  the 
heat  better. 

Charcoal  is  the  fuel  used  in  these  open  fires.  A  very  useful  accom- 
paniment to  these  portable  furnaces  is  a  piece  of  straight  stove-pipe, 
about  60  c.  m.  long  and  10  c".  m.  wide,  and  flaring  out  below  like  a 
funnel  until  it  is  wide  enough  to  cover  the  top  of  the  furnace.  This 
contrivance  powerfully  increases  the  draught,  and  is  used  to  urge  the 
fire  during  kindling,  or  to  intensify  it  while  a  fusion  is  in  progress. 
With  a  furnace  of  this  description  there  is  no  difficulty  in  keeping  a 
small  crucible  white-hot  for  a  short  time. 


XXXIV 


APPENDIX. 


FIG.  XXXV. 


Small     porcelain    crucibles    are    handled,   when  hot,  by  means 
FIG.  xxxiv.  of   small    steel    or   iron  tongs,  such  as    are 

represented  in   Fig.  XXXIV,  or  by  means 
of  small  steel  pincers,  such  as  are  used  by 
jewellers.     Larger  crucibles  are  handled  by  means  of  tongs  of  various 

shapes   and   sizes,  according  to 
the  weight  and   nature  of  the 
vessels  to  be  lifted.   Fig.  XXXV 
represents  two   good    forms  of 
stout  iron  tongs  for  lifting  large 
crucibles  out  of  a  coal  fire.    The 
manner  of  using  them  is  readily 
understood  from  the  figure. 
A  retort,  made  of  iron,  of  the  form  shown  in  Fig.  XXXVI,  is  a 
very  convenient  tool  in  making  large  quantities  of  oxygen,  and  in 
FIG.  xxxvi.  preparing  illuminating-gas  or  marsh-gas. 

The  iron  top  is  fitted  to  the  retort  with 
a  ground  joint  fastened  by  a  screw- 
clamp.  When  the  top  is  removed, 
the  whole  inner  surface  of  the  retort  is 
exposed,  —  a  decided  advantage  wher- 
ever the  residue  left  in  the  retort  after 
use  is  solid.  A  retort  of  about  300  c.  c. 
capacity  is  amply  large  for  most  uses. 
A  small  iron  kettle  makes  a  serviceable  retort  ;  the  lid  must  be  luted 
on,  and  the  nose  becomes  the  exit-tube. 

24.  Mortars.  —  Iron,  porcelain  and  agate  mortars  are  used  by 
chemists  to  reduce  solids  to  powder.  An  iron  mortar  is  useful  for 
coarse  work,  and  for  effecting  the  first  rough  breaking  up  of  sub- 
stances which  are  subsequently  powdered  in  the  porcelain  or  agate 
mortar.  If  there  be  any  risk  of  fragments  being  thrown  out  of  the 
mortar,  it  should  be  covered  with  a  cloth  or  piece  of  stiff  paper, 
having  a  hole  in  the  middle  through  which  the  pestle  may  be  passed. 
Pieces  of  stone,  minerals  and  lumps  of  brittle  metals  may  be  safely 
broken  into  fragments  suitable  for  the  mortar  by  wrapping  them  in 
strong  paper,  laying  them  so  enclosed  upon  an  anvil  and  striking 
them  with  a  heavy  hammer.  The  paper  envelope  retains  the  broken 
particles,  which  might  otherwise  fly  about  in  a  dangerous  manner,  and 
be  lost. 

The  best  porcelain  mortars  are  those  known  by  the  name  of  Wedge- 


APPENDIX.  xxxv 

wood-ware,  but  there  are  many  cheaper  substitutes.  Porcelain  mor- 
tars will  not  bear  sharp  and  heavy  blows  ;  they  are  intended  rather 
for  grinding  and  trituration  than  for  hammering  ;  the  pestle  may 
either  be  formed  of  one  piece  of  porcelain,  or  a  piece  of  porcelain 
cemented  to  a  wooden  handle  ;  the  latter  is  the  less  desirable  form  of 
pestle.  Unglazed  porcelain  mortars  are  to  be  preferred.  In  selecting 
mortars,  the  following  points  should  be  attended  to,  —  1st,  the  mortar 
should  not  be  porous  ;  it  ought  not  to  absorb  strong  acids  or  any 
colored  fluid,  even  if  such  liquids  be  allowed  to  stand  for  hours  in  the 
mortar  ;  2d,  it  should  be  very  hard,  and  its  pestle  should  be  of  the 
same  hardness  ;  3d,  it  should  be  sound  ;  4th,  it  should  have  a  lip  for 
the  convenience  of  pouring  out  liquids  and  fine  powders.  As  a  rule, 
porcelain  mortars  will  not  endure  sudden  changes  of  temperature. 
They  may  be  cleaned  by  nibbing  in  them  a  little  sand  soaked  in  nitric 
or  sulphuric  acid,  or,  if  acids  are  not  appropriate,  in  caustic  soda. 

Agate  mortars  are  only  intended  for  trituration  ;  a  blow  would 
break  them.  They  are  exceedingly  hard,  and  impermeable.  The 
material  is  so  precious  and  so  hard  to  work,  that  agate  mortars  are 
always  small.  The  pestles  are  generally  inconveniently  short,  —  a 
difficulty  which  may  be  remedied  by  fitting  the  agate  pestle  into  a 
wooden  handle. 

In  all  grinding  operations  in  mortars,  whether  of  porcelain  or  agate, 
it  is  expedient  to  put  only  a  small  quantity  of  the  substance  to  be 
powdered  into  the  mortar  at  once.  The  operation  of  powdering  will 
be  facilitated  by  sifting  the  matter  as  fast  as  it  is  powdered,  returning  to 
the  mortar  the  particles  which  are  too  large  to  pass  through  the  sieve. 

25.  Spatulse.  —  For    transferring  substances  in  powder,   or   in 
small  grains  or  crystals,  from  one  vessel  to  another,  spatulse  and 
scoops  made  of  horn  or  bone  are  convenient  tools.     A  coarse  bone 
paper-knife  makes  a  good   spatula  for  laboratory  use.     Cards,  free 
from  glaze  and  enamel,  are  excellent  substitutes  for  spatulee. 

26.  Thermometers.  —  Thermometers  intended  for  chemical  use 
must  have  no  metal,  and  no  wood  or  other  organic  material  upon 
their  outer  surfaces  ;  their  external  surfaces  must  be  wholly  of  glass. 
The  best  thermometers  are  straight  glass  tubes,  of  uniform  diameter, 
>vith  cylindrical  instead  of  spherical  bulbs,  and  having  the  scale  en- 
graved   upon  the   glass  ;    such   instruments  can   be   passed   tightly 
through  a  cork,  and  are  free  from  many  liabilities  to  error  to  which 
thermometers  with   paper   or  metal    scales  are  always  exposed.     A 
cheaper  kind  of  thermometer,  having  a  paper  scale  enclosed  in  a  glass 
envelope,  will  answer  for  most  experiments. 


xxxvi  APPENDIX. 


THE   METRICAL  SYSTEM  OF  WEIGHTS  AND   MEASURES. 

The  metrical  system,  employed  in  the  affairs  of  every-day  life  by 
most  of  the  nations  of  continental  Europe  and  by  scientific  writers 
throughout  the  world,  is  based  upon  a  fundamental  unit,  or  measure 
of  length,  called  a  metre.  This  metre  is  defined  as  the  40-millionth 
part  of  the  circumference  of  the  earth,  or,  in  other  words,  of  a  "  great 
circle "  or  meridian  ;  its  length  was  originally  determined  by  actual 
measurement  of  a  considerable  arc  of  a  meridian,  but  the  various 
measurements  heretofore  made  of  the  length  of  the  earth's  meridian 
differ  slightly  from  each  other,  and  it  is  to  be  expected,  and  indeed 
hoped,  that  the  steady  improvements  of  methods  and  instruments 
will  make  each  successive  determination  of  the  length  of  the  meridian 
better  than,  and  therefore  different  from,  the  preceding.  It  is,  on  this 
account,  necessary  to  define  the  standard  of  length,  by  legislation,  to 
be  a  certain  rod  of  metal,  deposited  in  a  certain  place  under  specified 
guaranties,  and  to  secure  the  uniformity  and  permanence  of  the 
standard  by  the  multiplication  of  exact  copies  in  safe  places  of  de- 
posit. 

From  this  single  quantity,  the  metre,  all  other  measures  are  deci- 
mally derived.  Multiplied  or  divided  by  10,  100,  1000,  and  so  forth, 
the  metre  supplies  all  needed  linear  measures,  and  the  square  metre 
and  cubic  metre,  with  their  decimal  multiples,  supply  all  needed 
measures  of  area  or  surface,  on  the  one  hand,  and  of  solidity  or 
capacity  on  the  other. 

From  the  unit  of  measure  to  the  unit  of  weight  the  transition  is 
admirably  simple  and  convenient.  The  cube  of  the  1 -hundredth  of 
the  linear  metre  is,  of  course,  the  millionth  of  the  cubic  metre  ;  its 
bulk  is  about  that  of  a  large  die  of  the  common  backgammon  board. 
This  little  cube  of  pure  water  is  the  universal  unit  of  weight,  a 
gramme,  which,  decimally  multiplied  and  divided,  is  made  to  express 
all  weights.  The  numbers  expressing  all  weights,  from  the  least  to 
the  greatest,  find  direct  expression  in  the  decimal  notation ;  the 
weights  used  in  different  trades  only  differ  from  each  other  in  being 
different  decimal  multiples  of  the  same  fundamental  unit  ;  and  in 
comparing  together  weights  and  volumes,  none  but  easy  decimal 
computations  are  ever  necessary. 


xxxvii 


The  nomenclature  of  the  metrical  system  is  extremely  simple  ;  one 
general  principle  applies  to  each  of  the  following  tables.  The  Greek 
prefixes  for  10,  100  and  1000,  viz.,  deca,  hecto  and  kilo,  are  used  to 
signify  multiplication,  while  the  Latin  prefixes  for  10,  100  and  1000, 
viz.,  deci,  centi  and  milli,  are  employed  to  express  subdivision.  Of 
the  names  thus  systematically  derived  from  that  of  the  unit  in  each 
table,  many  are  not  often  used  ;  the  names  in  common  use  are  those 
printed  in  small  capitals.  Thus  in  the  table  for  linear  measure,  only 
the  metre,  kilometre,  centimetre  and  millimetre  are  in  common  use,  — 
the  first  for  such  purposes  as  the  English  yard  subserves,  the  second 
instead  of  the  English  mile,  the  third  and  fourth  in  lieu  of  the  frac- 
tions of  the  English  foot  and  inch. 


LINEAR  MEASURE. 

Metre. 

(  MILLIMETRE 

__ 

0.001  or  1-1,000  of  a  metre. 

Divisions 

.  <  CENTIMETRE 

_ 

0.01     or  1-100 

(  Decimetre 

— 

0.1      or  1-10            " 

Unit     . 

.      METRE 

= 

1. 

(  Decametre 

— 

10. 

Multiples 

.  <  Hectometre 

•ec 

100. 

(  KILOMETRE 

= 

1,000. 

Divisions 
Unit    . 


SURFACE  MEASURE. 


(  Millimetre  square 

<  Centimetre  square 

(  Decimetre  square 

METRE  SQUARE 


0.000,001  of  a  metre  square. 
0.000,1          "  " 

0.01  " 

1. 


CUBIC   MEASURE. 


Divisions 
Unit    . 
Multiples 


(  Cubic  Millimetre 

<  Cubic  Centimetre 
(  Cubic  Decimetre 

CUBIC  METRE 
f  Cubic  Decametre 

<  Cubic  Hectometre 
I  Cubic  Kilometre 


Cubic  Metre. 
0.000,000,001 
0.000,001 
0.001 
1. 

1,000. 

1,000,000. 

1,000,000,000. 


The  table  for  land  measure  we  omit,  as  having  no  connection  with 
our  subject.  For  the  measurement  of  wine,  beer,  oil,  grain  and  simi- 
lar wet  and  dry  substances,  a  smaller  unit  than  the  cubic  metre  is 
desirable.  The  cubic  decimetre  has  been  selected  as  a  special  stand- 
ard of  capacity  for  the  measurement  of  substances  such  as  are  bought 
and  sold  by  the  English  wet  and  dry  measures.  The  cubic  decimetre 
thus  used  is  called  a  litre. 
28 


XXXV111 


APPENDIX. 


CAPACITY  MEASURE. 


Divisions 
Unit    . 
Multiples 


( Millilitre  == 

<  Centilitre  = 
(Decilitre  = 

LITRE  = 

C  Decalitre  = 

<  HECTOLITRE  = 


Litres. 

0.001 

0.01 

0.1 

1. 

10. 

100. 


(Kilolitre         =1,000. 


Cubic  Metre. 

0.000,001  =  1  cubic  centimetre. 

0.000,01 

0.000,1 

0.001 

0.01 

0.1 

1. 


—  1  cubic  decimetre. 


=  1  cubic  metre. 


The  table  of  weights  bears  an  intimate  relation  to  this  table  of 
capacity.  As  already  mentioned,  the  weight  of  that  die-sized  cube,  a 
cubic  centimetre  or  millilitre  of  distilled  water  (taken  at  4°,  its  point 
of  greatest  density)  constitutes  the  metrical  unit  of  weight.  This 
weight  is  called  a  gramme.  From  the  very  definition  of  the  gramme, 
and  from  the  table  of  capacity-measure,  it  is  clear  that  a  litre  of  dis- 
tilled water  at  4°  will  weigh  1,000  grammes. 

WEIGHTS. 

Grammes. 

C  MILLIGRAMME  =  0.001 

Divisions    .  <  CENTIGRAMME  =  0.01 

(DECIGRAMME  =  0.1 

Unit    .       .      GRAMME  1.     =  1  cubic  centimetre  of  water  at  4°. 

( Decagramme  =  10. 

Multiples  .  <  Hectogramme  =  100. 

(Kilogramme  =  1,000.     =  1  cubic  decimetre  of  water  at  4°. 

The  simplicity  and  directness  of  the  relations  between  weights  and 
volumes  in  the  metrical  system  can  now  be  more  fully  explained. 
The  chemist  ordinarily  uses  the  gramme  as  his  unit-weight,  and  for 
his  unit  of  volume  a  cubic  centimetre,  which  is  the  bulk  of  a  gramme 
of  water.  For  coarser  work,  the  kilogramme  becomes  the  unit  of 
weight,  and  the  corresponding  unit  of  measure  is  the  litre,  which  is 
the  bulk  of  a  kilogramme  of  water.  In  commercial  dealings,  in 
manufacturing  processes,  and  above  all  in  scientific  investigations, 
these  simple  relations  between  weights  and  measures  have  been  found 
to  be  an  inestimable  advantage.  The  numerical  expressions  for 
metrical  weights  and  measures  may  always  be  read  as  decimals. 
Thus  5.126  metres  will  be  read  five  metres  and  one  hundred  and 
twenty-six  thousandths,  and  not  five  metres,  one  decimetre,  two  cen- 
timetres and  six  millimetres.  The  expression  10.5  grammes  is  read 
ten  and  five-tenths  grammes  ;  just  as  we  say  one  hundred  and  five 
dollars,  not  ten  eagles  and  five  dollars  ;  or  sixty-five  cents,  not  six 
dimes  and  five  cents.  All  computations  under  the  metrical  system 
are  made  with  decimals  alone. 


APPENDIX. 


xxxix 


The  abbreviations  commonly  met  with  in  chemical  literature  are  :  — 


m.  m.  for  millimetre  ; 
m.  for  metre  ; 
grm.  for  gramme  ; 


c.  m.  for  centimetre  ; 

c.  c.  or  c.  m?  for  cubic  centimetre  ; 

kilo,  for  kilogramme. 


The  equivalents  in  English  weights  and  measures  of  those  metrical 
weights  and  measures  which  are  used  in  chemistry  can  be  readily 
found  by  the  aid  of  the  table  on  the  following  page,  which  is  available 
not  only  for  grammes,  centimetres  and  litres,  but,  by  mere  change  of 
the  position  of  the  decimal  point,  for  all  decimal  multiples  or  subdi- 
visions of  these  quantities. 


One  cubic  metre 

decimetre  (  a  litre) 
centimetre 
litre 


One  pound  avoirdupois 
11       "       troy 
11    ounce  avoirdupois 

"      troy 
grain 

English  imperial  gallon 
U.  S.  standard  gallon 
foot 
yard 


35.31660  cubic  feet. 

61.02709  "      inches. 

0.06103  " 

0.22017  imp.    gallon. 

0.88066  "     quart. 

1.76133  "     pint. 

0.26427  U.  S.  gallon. 

1.05708  "   "  quart. 

2.11415  "   "  pint. 


7000     grains 
5760         " 
437.5       " 


=      453.59  grm. 
=      373.24    " 


277.274  cu.  in.     = 


31.10    " 
64.80  mgrm. 
4.54  litres. 
3.78     " 

=         0.3048  metre. 
=         0.914*  mgrm. 


xl 


THE  METRICAL   SYSTEM. 


V* 

~  *B 

L 

- 

H 
K 

H 

- 

M 

H 

o 

H 

ft 

«j 
H 

PH      m 

H     » 

H 

i 

^ 

1  . 

O 

g 

o 

CO 

-« 

W 

e* 

H 

APPENDIX. 


xli 


TABLE  —  For  the  Conversion  of  Degrees  on  the  Centigrade  Thermometer  into 
,  Degrees  of  Fahrenheit's  Scale. 


Cent 

Fahr. 

Cent. 

Fahr. 

Cent. 

Fahr. 

o 

—50 

—58.0 

17° 

62°.6 

60° 

140.0 

—45 

—49.0 

18 

64.4 

61 

141.8 

—40 

—40.0 

19 

66.2 

62 

143.6 

—35 

—31.0 

20 

68.0 

63 

145.4 

—30 

—22.0 

21 

69.8 

64 

147.2 

—25 

—13.0 

22 

71.6 

65 

149.0 

—20 

-  4.0 

23 

73.4 

66 

*  150.8 

—19 

—  2.2 

24 

75.2 

67 

152.6 

—18 

-  0.4 

25 

77.0 

68 

154.4 

—17 

+  1-4 

26 

78.8 

69 

156.2 

—16 

3.2 

27 

80.6 

70 

158.0 

—15 

5.0 

28 

82.4 

71 

159.8 

—14 

6.8 

29 

84.2 

72 

161.6 

-13 

8.6 

30 

86.0 

73 

163.4 

—  12 

10.4 

31 

87.8 

74 

165.2 

—11 

12.2 

32 

89.6 

75 

167.0 

—10 

14.0 

33 

91.4 

76 

168.8 

—  9 

15.8 

34 

93.2 

77 

170.6 

—  8 

17.6 

35 

95.0 

78 

172.4 

-  7 

19.4 

36 

96.8 

79 

174.2 

-  6 

21.2 

37 

98.6 

80 

176.0 

—  5 

23.0 

38 

100.4 

81 

177.8 

-  4 

24.8 

39 

102.2 

82 

179.6 

-  3 

26.6 

40 

104.0 

83 

181.4 

-  2 

28.4 

41 

105.8 

84 

183.2 

-  1 

30.2 

42 

107.6 

85 

185.0 

0 

32.0 

43 

109.4 

86 

186.8 

-f  1 

33.8 

44 

111.2 

87 

188.6 

2 

35.6 

45 

113.0 

88 

190.4 

3 

37.4 

46 

114.8 

89 

192.2 

4 

39.2 

47 

116.6 

90 

194.0 

5 

41.0 

48 

118.4 

91 

195.8 

6 

42.8 

49 

120.2 

92 

197.6 

7 

44.6 

50 

122.0 

93 

199.4 

8 

46.4 

51 

123.8 

94 

201.2 

9 

48.2 

52 

125.6 

95 

203.0 

10 

50.0 

53 

127.4 

$6 

204.8 

11 

51.8 

54 

129.2 

97 

206.6 

12 

53.6 

55 

131.0 

98 

208.4 

13 

55.4 

56 

132.8 

99 

210.2 

14 

57.2 

57 

134.6 

100 

212.0 

.  15 

59.0 

58 

136.4 

16 

60.8 

59 

138.2 

28  * 


ORDER-LIST  OF  CHEMICALS. 


THE  quantities  here  given  are  the  quantities  which  one  person  will 
use  in  performing  the  numbered  experiments  of  this  manual  accord- 
ing to  the  directions.  In  ordering  chemicals  for  a  class  of  several 
students,  a  small  reduction  may  be  made  upon  the  multiplied  quanti- 
ties. Teachers  can  get  some  idea  of  the  cost  of  these  chemicals  by 
referring  to  the  price  lists  of  the  "  Druggists'  Circular,"  published 
monthly  at  36  Beekman  Street,  New  York,  price  13  cents.  The 
names  by  which  the  substances  are  known  in  commerce  are  given  in 
the  following  list ;  such  substances  as  sugar,  starch,  marble,  &c., 
do  not  appear  in  the  list  :  — 


Alcohol 5  oz. 

Alum |  oz. 

Ammonia- water  (Aqua  Am- 
monia)      6  oz. 

Ammonium   chloride    (sal 

ammoniac)  1  oz. 

Ammonium  nitrate  .     .     .     J  oz. 

Aniline a  few  drops 

Aniline  red  .  .  a  small  crystal 
Antimony,  metallic  .  .  30  grains 
Arsenious  acid  ...  30  grains 
Barium  chloride  .  .  a  few  grains 

Benzol f  oz. 

Bleaching-powder     .     .     .     2  oz. 

Bone-black 3  oz. 

Bromine      .     .     .     .  a  IV  w  drops 
Calcium  chloride      .     .     .  1£  oz. 
Calcium     sulphate     (gyp- 
sum) ....       a  few  grains 

Camphor iV  oz> 

Castor  oil 3J  oz. 


Carbolic  acid  (crystallized)  J  oz. 
Carbon  bisulphide  (bisul- 

phuret  of  carbon)  .  .  .  |  oz. 
Chalk,  powdered  .  .  .  ^  oz. 
Chlorhydric  acid  .  .  .  1  Ib. 

Cochineal 30  grains 

Copper  (filings)  .  .  .  .  Ij  oz. 
Copper  oxide  ...  30  grains 
Copper  sulphate  (blue 

vitriol) 30  grains 

Ether 1  oz. 

Fluor-spar  ^  oz. 

Gold-leaf  .  .  .  .  1  sq.  inch 

Gum-arabic ^  oz. 

Indigo 50  grains 

Iodine 10  grains 

Iron  (filings) 1  oz. 

Iron  sulphate  (copperas)  .  %  oz, 
Iron  sulphide  .  .  .  .  1  oz, 
Lead  acetate  (sugar  of  lead)  %  oz, 
Lead  oxide  (litharge)  .  .  2  oz 


ORDER-LIST  OF  CHEMICALS. 


Litmus        15  grains 

Logwood,  extract  of  .  30  grains 
Magnesium  wire  .  .  4  inches 
Manganese,  black  oxide  of  1  oz. 
Mercury  chloride  (corrosive 

sublimate)     ...  a  few  grains 
Mercury,  red  oxide  of  .     .     f  oz. 

Nitric  acid 6  oz. 

Nitric  acid  (fuming)     .     .     j  oz. 

Nutgalls \  oz. 

Oxalic  acid  ....  50  grains 
Phosphorus,  1  stick,  2^  inches  long 
Picric  acid  .  .  .  .30  grains 
Platinum,  scrap  .  .  .10  grains 
Potassium,  2  pieces  the  size  of  a 

pea. 

Potassium  bichromate  .  .  ^  oz. 
Potassium  bromide  .  .  1  grain 
Potassium  chlorate  .  .  .  £  oz. 
Potassium  cyanide  .  .  30  grains 
Potassium  ferrocyanide  (yel- 
low prussiate  of  potash)  %  oz. 
Potassium  hydrate  (white 

caustic  potash)        .     .     .     |  oz. 
Potassium  iodide      •     •     •  iV  oz- 
Potassium     nitrate     (salt- 
petre)        3  oz. 

Phosphorus,  red  .     .     .15  grains 


Potassium  permanganate  6  grains 
Potassium  tartrate  (cream 

of  tartar)      '.....     1  oz. 

Rosin     ......  30  grains 

Shellac   ......  40  grains 

Sodium,   2  pieces  the  size  of  a 

pea. 

Sodium  acetate  ...  30  grains 
Sodium  biborate  (borax)  .  ^  oz. 
Sodium  carbonate  .  .  .  ^  oz. 
Sodium  hydrate  (caustic 

soda)   .......     1  oz. 

Sodium      silicate,     strong 

solution  (water-glass)      .     1  oz. 
Sodium  sulphate  (Glauber's 

salt)     .......     1  oz. 

Strontium  nitrate  .  a  few  grains 
Sulphur,  flowers  of  .  .  .  1  oz. 
Sulphur,  roll  brimstone  .  4  oz. 
Sulphuric  acid  ...  1^  Ibs. 
Tin  binoxide  .  .  .15  grains 


Turpentine,  crude  ... 
Turpentine,  oil  of  ... 
Zinc,  granulated  or  scraps 
Zinc  filings  (or  dust)  .  . 
Zinc  sheet,  two  strips  6 
inches. 


1  oz. 
4  oz. 
2  oz. 
-^  oz. 
by  2 


ORDER-LIST   OF   UTENSILS. 

THE  following  list  includes  the  utensils  which  one  person  will  need 
in  performing  all  the  numbered  experiments  in  this  manual.  The 
principal  articles  of  steady  consumption  are  glass-tubing,  retorts, 
flasks,  corks,  caoutchouc-connector  and  filter-paper.  Many  of  the 
other  articles,  once  obtained,  last  a  long  time.  It  is  evidently  not  ne- 
cessary to  provide  all  this  apparatus  for  every  member  of  a  large  class. 
Six  retorts,  as  many  Woulffe-bottles,  four  soda-water  bottles,  two  or 
three  measuring  glasses,  two  mortars,  two  pipettes,  one  blast-lamp  and 
bellows,  three  or  four  pieces  of  platinum  foil,  two  thermometers,  one 


xliv 


ORDER-LIST  OF  UTENSILS. 


pair  of  scales  and  one  set  of  weights  will  suffice,  if  used  with  method, 
for  a  class  of  twenty  or  twenty-five  students.  Many  of  the  article? 
can  be  obtained  of  the  wholesale  druggists  or  of  dealers  in- hardware  : 
for  the  rest,  teachers  can  consult  the  priced  catalogues  of  the  dealers 
in  philosophical  apparatus  and  chemical  ware.  T9^  *. 


Glass-tubing  (App.  Fig.  1)  — 

1  stick  about  3  ft.  long  of  No.  1 


i   " 
t  " 


2 


"  3 

"  4 

"  5 

"  7 


1  tube  about  1  foot  long  and  1 

inch  in  internal  diameter. 

[If  ignition  -tubes  can  be  bought 

ready  made,  a  dozen  of  them  may 

be  bought  instead  of  one  stick  of 

No.  1  and  one  stick  of  No.  2  tub- 

ing-] 

1  retort  of   12  oz.  capacity  with 

glass  stopper. 
1  receiver  of  8  or  10  oz.  capacity 

with  tubulure. 
Bottles  — 

1  wide-mouth  bottle,  |  gallon. 

1      "         "          "        1  quart. 

1  "         "          "1  pint. 

2  "         "          «        8oz. 
2      "         "          "        4  oz. 
2      "         "          "        2oz. 

1  stout  pint  bottle  with  mouth 
about  an  inch  across,  for  hy- 
drogen generator. 
[These    bottles    may  be   of  a 
very  common  quality,  such  as  are 
sold  as  "  packing  "  bottles.] 
Funnels  — 

1  four  inches  in  diameter. 
1  two  inches  in  diameter. 


3  Woulffe-bottles  of  about  12  oz. 

capacity. 
Glass  flasks  — 

1  of  1J  pints'  capacity 

1  of  8  oz.  capacity. 

2  of  4  oz.  capacity. 
2  of  2  oz.  capacity. 

1  thistle-tube. 

1  soda-water  bottle,  stout. 

1  conical  wine-glass. 

6  test-tubes. 

1  drying-tube. 

1  measuring-glass    of    250    c.    c. 

capacity  grad.  for  every  10  c.  c. 
1  measuring-glass  of  25  or  30  c.  c. 

capacity    graduated    to     cubic 

centimetres. 
1  small  pipette. 

1  nest  of  4  or  5  beakers,  of  which 
the  largest  is  of  250  c.  c.  capa- 
city. 

2  or  3  bits    of    window-glass,   3 
inches  square. 

Porcelain  evaporating-dishes  — 

1  about  4  inches  diameter. 

1  about  2^  inches  diameter. 

1  deep  dish    (App.    §  21)    of 

500  c.  c.  capacity. 
1  small  iron  mortar. 
1  Wedge  wood    mortar    about    4 

inches  in  diameter. 
1  Bunsen  gas-lamp  with  blowpipe 

tube  (or  spirit-lamp  where  gas 

is  not  to  be  had.) 
1  small  spirit-lamp. 


ORDER- LIST  OF  UTENSILS. 


xlv 


1  iron  ring-stand. 

1  piece  of  iron  wire-gauze  about 

4  inches  square. 
4  or  5  feet  of  stout  iron  wire. 
4  feet  iron  piano- wire. 
1  piece    fine    brass     (or    copper) 

gauze  about  2|  inches  square. 
1  iron    sand-bath    4£   inches    in 

diameter. 

1  water-bath  (App.  §  17). 
1  glass-blower's  lamp  or  Bunsen's 

gas  blast-lamp. 

1  small  double  acting  bellows. 
1  mouth-blowpipe. 
1  triangular  file. 
1  round  file. 

1  pair  jewellers'  tweezers. 
1  piece  platinum  foil  l£  inches 

square. 
1  piece    platinum    wire  4  inches 

long,  and  not    thicker   than  a 

No.  5  needle. 
1  stoneware  milk-pan. 
1  flower-pot  saucer   (or  two  bits 

of  wood  6  inches  by  3  inches 

by  1  inch,  loaded  with  lead). 


1  Hessian  crucible  of  about  8  oz. 
capacity. 

1  lead  pan  for  Exp.  41. 

1  common  plate. 

1  soup  plate. 

1  thermometer. 

1  pair  of  small  scales  ("Tea"- 
scales  for  grocers'  use). 

1  set  of  gramme  weights  1,  2,  5, 
10,  20  and  50  grammes. 

Corks  —  an  assortment  of  various 
sizes,  to  fit  the  ignition-tubes, 
the  flasks,  the  hydrogen  gen- 
erator, &c. 

Caoutchouc  tubing  — 
1  foot  of  %  inch. 
1  foot  of  yV  inch. 
4  feet  of  £  inch. 

1  iron  spoon. 

1  pair  wooden  nippers. 

4  sheets  of  common  filter-paper, 
or  2  sheets  of  filter-paper  and 
half  a  bunch  of  cut  filters  3 
inches  in  diameter. 


INDEX. 


The  following  abbreviations  are  used  in  this  index  ;  occ.  stands 
for  occurrence  ;  prep,  for  preparation  ;  prop,  for  properties  ;  comp.  for 
composition ;  def.  for  definition.  The  numbers  refer  to  the  pages ; 
the  Roman  numerals  to  the  Appendix. 


ACETATES,  153. 
Acetic  acid,  151. 

glacial,  153. 

prep,  from  wood,  152,  173. 

from  alcohol,  151. 
Acetic  ether,  150. 
Acetylene,  175. 
Acetylene  series,  175. 
Acid,  acetic,  151. 

antimonic,  106. 

arable,  188. 

arsenic,  105. 

arsenious,  104. 

benzoic,  175. 

bromhydric,  62. 

bromic,  62. 

caffeo-tannic,  195. 

carbolic,  170. 

carbonic,  119. 

chlorhydric,  49-52. 

chloric,  60. 

chromic,  262. 

citric,  194. 

cyanhydric,  136. 

ferri-cyanhydric,  225. 

ferro-cyanhydric,  224. 

fluorhydric,  66. 

fluosilicic,  206. 

formic,  153. 

gallic,  196. 


Acid,  gallo-tannic,  195. 
hypochlorous,  60. 
iodic,  64. 
iodohydric,  64. 
lauric,  159. 
malic,  193. 
manganic,  263. 
meconic,  196. 
nitric,  39. 
oleic,  155. 
oxalic,  192. 
palmitic,  155. 
pectic,  189. 
pectosic,  189. 
phenic,  170. 
phosphoric,  98. 
picric,  171. 
pyroligneous,  153. 
querci-taflnic,  195. 
resinic,  190. 
selenic,  86. 
silicic,  205. 
stannic,  281. 
stearic,  155. 
succinic,  191. 
sulphindigotic,  199. 
sulphuric,  81. 
sulphurous,  78. 
tannic,  194. 
tartaric,  193. 


xlviii 


INDEX. 


Acid,  tri-nitro-phenic,  171. 
Acid,    meanings    of    the    term, 
41-43. 

reaction,  40. 

Acids  and  bases,  relation  between, 
42. 

bases  and  salts,  41. 

vegetable,  191. 
Action  of  air  and  water  on  lead, 

249. 

Acrolein,  157. 
Air,  a  mixture,  38. 

analysis  of,  6,  7. 

chemical  prop,  of,  6. 

.comp.  of,  6-8. 

displacing  of,  5. 
"not  an  element",  8. 

physical  prop,  of,  5. 

presence  of,  4. 

reaction    with  nitric  oxide, 
38. 

weight  of,  5. 
Albumin,  201., 

vegetable,  201. 
Alcohol,  absolute,  146. 

amyl,  148. 

di  -  atomic,   tri-  atomic,   &c., 
165. 

def.  of  term,  165.    . 

inflammability  of,  127. 

methyl,  148. 

produced    by    fermentation, 
143. 

prop,  of,  144. 

separation  of  by  distillation, 
145. 

uses  of,  147. 

Alcohol-lamp  flame,  126: 
Alcohols,  148. 
Aldehyde,  152,  262. 
Ale,  182. 
Alizarin,  197. 
Alkali  group,  240. 

metals,  240. 
Alkalies,  229. 
Alkaline  reaction,  41. 
Alkaloids,   organic,  absorbed    by 
charcoal,  118. 

vegetable,  196.          ....... 

Allotropism,  68. 


Alum,  260. 

in  bread,  214. 
Alum,  ammonium,  261. 
Alum-cake,  260. 
Alumina,  258. 
Aluminates,  259. 
Aluminum,  abundance  of,  258. 

alloys  of,  258. 

bronze,  258. 

hydrate,  259. 

combines  with   coloring 

matters,  259. 
used  as  a  mordant,  260. 

oxide,  258, 

prop,  of,  258. 

silicates,  261. 

sulphate,  260-. 

Amalgams,  279.      

Amber,  191. 

Amide,  term  denned,  169. 
Amine,  term  defined*  169., 
Ammonia,  comp.  of,  .46. 

liquid,  45.         .,      . 

occ.  of,  47.       .  .   . 

physical  prop,  of,  45. 

prep,  of,  44.   . 

solubility  in  water,  45. 

sources  of,  47,  . .  .,  '..,-;. 

Ammoniacal  liquor  of  gas-works, 

47. 
Ammonia- water,-  formula  of,  46. 

precipitates      metallic    :  hy- 
drates, 229. 

prep,  of,  48. 

uses  of,  48. 
Ammonium,  hypothetical,  49,  228. 

carbonates,  230.     " ,'..  u 

chloride,  229.    .       ...-., 

hydrate,  229..       - 

nitrate,  230.  ;.       ; 

decomposition  of,  31. 
prep,  of,  46. 

sulphate,  230. 

sulphides,  231.     - 

sulphydrate,  231.- 
Ammonium-salts,  prop,  of,-  47. 

source  of,  .229. 

test  for,  229.       .  . 
Ampere,  law  of,  89.    .  •• 

Amygdalin,  174. 


INDEX. 


xlix 


Amyl  alcohol,  148. 
Analysis,  def.  of,  3. 
Anhydride,  def.  of,  36,  44. 
antimonic,  106. 
arsenic,  105. 
arsenious,  103. 
boraeie,  208. 
carbonic,  119. 
chromic,  262. 
hypophosphorous,  97. 
manganic,  263. 
nitric,  36. 
phosphoric,  98. 
phosphorous,  97. 
silicic,  205. 
sulphuric,  81. 
sulphurous,  75,  78. 
Anhydrite,  245. 
Aniline  colors,  169. 
Aniline,  comp.  of,  169. 
compounds,  169. 

action    of    oxygen     on, 

170. 

prep,  of,  168.  . 
prop,  of,  168. 
Animal      charcoal,     decolorizing 

power  of,  117. 
Anthracene,  173. 
Anthracite,  111. 

conducts  heat,  112. 
Antimonic  acid,  106. 
Antimony,  alloys  of,  105. 
glance,  107. 
mirrors,  106. 
occ.  of,  105. 
prop,  of,  105. 
sulphide,  107. 
terchloride,  106. 
teroxide,  106. 
Antiseptic  agents,  204. 

carbolic  acid,  171. 
common  salt,  211. 
dead  oil  of  tar,  171. 
kreasote,  174. 
mercuric  chloride,  279. 
sugar,  204. 
wood  smoke,  174. 
Antozone,  71. 

fogs  and  smokes,  71. 
Aqua  regia,  53. 

29 


Arabic  acid,  188. 

Argol,  193. 

Arrow-root,  184. 

Arseniates,  105. 

Arsenic,  detection  of  the  poison, 

103. 

greens,  104. 
mirrors,  103. 
occ.  of,  102. 
prop,  of,  102. 
sulphides  of,  105. 
Arsenic  acid,  105. 
Arsenious  acid,  103. 

antidote  for,  104. 
a  poison,  104. 
reduction  of,  104. 
solubility  of,  103. 
sources  of,  103. 
Arsenites,  104. 
Arseniuretted  hydrogen,  102. 
Artificial  fats,  159. 

light,  125. 
Atom,  def.  of,  18. 
Atomic  weights,  def.  of,  19. 
practical  use  of,  54. 
table  of,  289. 

Atoms,  absolute  size  of,  19. 
relative  size  of,  18. 

BALSAMS,  189. 
Barium,  247. 

compounds,  247. 

flame,  248. 
Barley  sugar,  179. 
Barytes,  247. 
Base,  169. 

def.  of,  41,  43. 
Bases,  organic,  190. 
Bayberry  tallow,  159. 
Beakers,  xxix. 
Beef  tallow,  154. 
Beer.  182. 
Beeswax,  158. 
Beet-sugar,  178. 
Bell-metal,  275. 
Bellows,  x. 
Benzoic  acid,  175. 
Benzol,  comp.  of,  167. 

dissolves  grease,  167. 

obtained  from  coal-tar,  166. 


INDEX. 


Benzol,   present  in    illuminating 
gas,  141. 

prop,  of,  166. 
Bessemer  steel,  268. 
Bibasic  acids  denned,  85. 
Bismuth,  makes    fusible     alloys, 
107. 

oxides  of,  107. 

prop,  of,  107. 

Bitter  almonds,  oil  of,  174. 
Bituminous  coal,  111. 
Bivalent  metals,  53,  250. 
Black  ball,  212. 
Black  lead,  110. 
Blast  furnace,  iron,  working   of, 

265. 
Bleaching  by  chloride  of  lime,  61. 

by  chlorine,  59. 

by  ozone,  69. 

by  sulphurous  acid,  80. 
Bleaching- powder,  60. 
Blende,  252. 
Bloom,  264. 
Blowers,  x. 
Blowpipe,  Bunsen's  gas,  ix. 

mouth,  use  of,  129. 

oxidizing  flame  of,  130. 

oxy-hydrogen,  27,  129. 

reducing  flame  of,  130. 
Blowpipes,  mouth,  xi. 
Blue  vitriol,  277. 
Bone-black,  prep,  of,  119. 
Bone-phosphate  of  calcium,  246. 
Boracic  acid,  extraction  of,  208. 

prop,  of,  208. 
Boracic  anhydride,  208. 
Borax  as  a  blowpipe  test,  217. 

uses  of,  218. 
Boron,  allotropic  states  of,  208. 

occ.  of,  207. 
Brass,  275. 
Bread,  185. 

raising  with  chemicals,  214. 
Britannia  metal,  105. 
Bromates,  62. 
Bromhydric  acid,  62. 
Bromic  acid,  62. 
Bromine,  61. 
Bronze,  275. 
Browii  sugar,  177. 


Brucine,  196. 
Bulbs,  blowing,  vi. 
Bunsen's  burner,  126,  vi. 
Butter,  202. 

constitution  of,  155. 

CADMIUM,  occ.  of,  257. 
sulphide,  257. 
symbol  of  atom  and  molecule 

the  same,  91. 
Caesium,  233. 
Caffeine,  197. 
Caffeotannic  acid,  195. 
Calcium,  241. 
flame,  248. 
light,  28. 

carbonate,  occ.  of,  241. 
solubility  of,  242. 
chloride,  246. 

used    for  drying  gases, 

246. 

hydrate,  243. 
hypochlorite,  60,  247. 
oxide,  242. 

infusible,  243. 
phosphates,  92,  246. 
sulphate,  245. 
Calc-spar,  241. 
Calomel,  279. 
Camphor,  prop,  of,  162. 
Candles,  manufacture  of,  158. 
Cane-sugar,  176. 
Caoutchouc,  190. 

stoppers  and  tubing,  xi,  xii. 
Caramel,  179. 
Carbolates,  171. 

antiseptic  prop,  of,  171. 
used  as  disinfectants,  171. 
Carbolic  acid,  170. 
Carbon,   allotropic    modifications 

of,  109. 

Carbon  bisulphide,  135. 
prop,  of,  135. 
uses  of,  135. 
protoxide,  123. 
a  poison,  123. 
prep,  of,  128. 
prop,  of,  123. 
a  reducing  agent,  124. 
Carbonates,  119. 


INDEX. 


li 


Carbonic  acid,  119. 

extinguishes       combus- 
tion, 121. 

formed    in    combustion, 
119. 

in  fermentation,  122. 
in  respiration,  122. 
generator,  120. 
liquid,  121. 

obtained    from    carbon- 
ates, 120. 
prop,  of,  119. 
solid,  121. 
solubility  of,  121. 
spec,  gravity  of,  121. 
test  for,  119. 
Carbonic  anhydride,  see  Carbonic 

acid. 

Carbonic  oxide,  see  Carbon  prot- 
oxide. 

Carmine,  197. 
Carmine-lake.  259. 
Casein,  201. 
Cast  iron,  impurities  of,  266. 

varieties  of,  266. 
Caustic  potash,  221. 
Caustic  soda,  215. 

manufacture  of,  216. 
Cellulose,  186. 
Cementation  process,  267. 
Cerium,  274. 
Chalk,  241. 

Charcoal,  absorbs  different  gases 
in     different    proportions, 
116. 
causes  combination  of  gases, 

117. 

a  disinfectant,  116. 
prep,  of,  112. 
a  reducing  agent,  115. 
removes  colors.  117. 
stability  of,  116. 
Cheese,  202. 
Chemical  changes,  2. 
combination,  6. 
compounds  and    mechanical 

mixtures,  37. 
equations,  24. 
symbols,  24. 
Chemistry,  agricultural,  200. 


Chemistry,  physiological,  200. 

stellar,  233. 

subject  matter  of,  1. 
Chimneys  create  draughts,  131. 

on  fire,  how  to  put  out,  79. 

use  of,  130. 
Chinese  wax,  158. 
Chitin,  202. 
Chloral,  152. 
Chlorates,  60. 

Chlorhydric  acid,  24,  49-52. 
a  gas,  50. 
comp.  of,  24,  50. 
gas,  prep,  of,  50. 
prep,  of,  52. 
prop,  of,  50. 
Chloric  acid,  60. 
Chloride  of  lime,  247. 
Chlorides,  formation  of,  53. 
Chlorine,  acids  and  oxides  of,  60. 

atomic  weight  of,  56. 

bleaches,  59. 

burns  in  hydrogen,  58. 

combustion  in,  57,  58. 

decomposes  water,  59. 

disinfects,  60. 

explosive   mixture  with  hy- 
drogen, 56. 

group,  65. 

occ.  of,  55. 

physical  prop,  of,  56. 

prep,  of,  56. 

prep,    from  bleaching   pow- 
der, 60. 

test  for,  63. 

unites  with  metals,  57. 

water,  59. 
Chloroform,  formula  of,  139. 

prep,  of,  139. 
Chromates,  262. 
Chrome  alum,  262. 

iron  ore,  261. 
Chromic  acid,  262. 
Chromic  anhydride,  262. 
Chromium,  occ.  of,  261. 
Chromium  hydrate,  262. 

sesquioxide,  262. 

sulphate,  262. 
Cinchonine,  197. 
Cinnabar,  277,  278. 


lii 


INDEX. 


Citric  acid,  194. 

Classification  of  the  elements,  287. 

Clay,  261. 

Cleavage,  74. 

Cloves,  oil  of,  160. 

Coal,  bituminous,  111. 

distillation  of,  111. 
Coal-gas,  comp.  of,  131. 

prep,  of,  139. 

purification  of,  141. 
Coal-tar,  141,  166. 

distillation  of,  166. 
Coal-tar  naphtha,  166. 
Cobalt,  273. 

Cochineal,  tincture,  prep,  of,  197. 
Coke,  111. 

conducts  heat,  112. 
Collodion,  187. 

used  in  photography,  238. 
Coloring  matters,  organic,  197. 
Columbium,  295. 
Combination  by  volume,  87. 
Combining  weights  of  compounds, 
43. 

and  unit- volume  weights 

compared,  292. 
Combustibles,  and  supporters  of 

combustion,  29. 
Combustion,  def.  of,  11,  58. 

ordinary,  124-132. 

spontaneous,  160,  273. 
Condensation-ratios,  88. 
Condenser,  146. 

Cooling  flames  by  good  conduct- 
ors, 134. 
Copper,  alloys  of,  275. 

occ.  and  prop,  of,  274,  275. 

pyrites,  274. 
Copper,  acetates,  277. 

hydrate,  276. 

oxides,  275. 

sulphate,  27.7. 
Copperas,  270. 
Cork-cutters  or  borers,  xiii. 
Corks,  xii. 

Corrosive  sublimate,  279. 
antidote  for,  279. 
Cream  of  tartar,  193. 
Crucibles,  Hessian,  xxxiii. 

porcelain,  xxxii. 


Cryolite,  66. 
Crystallization,  by  fusion, 

solution,  74. 

sublimation,  75. 

six  systems  of,  74. 
Crystals,  methods  of  forming,  74 
Cyanates,  137. 

Cyanhydric  acid,  136.         ^vislia 
Cyanides,  136.  .;,9l3 

Cyanogen,  136. 

DEAD  OIL  of  tar,  171. 

Decay  of  organic  substances,  203. 

Decolorizing  power  of    charcoal, 

117. 

Definite  proportions,  30. 
Deflagrating  spoon,  xxii. 
Deflagration,  226. 
Deodorizing  by  charcoal,  117. 
Detection  of  arsenic,  103. 
Developers,  a  term   of  photogra- 

phy, 239. 
Dextrine,  184. 
Dextrose,  179. 
Diamond,  109. 

Diamond,  combustion  of,  110. 
Diachylon,  156. 
Didymium,  274. 
Diffusion  of  gases,  26. 

relative  rapidity  of,  26. 
Dimorphous    substance,    defined, 

75. 
Disinfectant,  charcoal,  116. 

zinc  chloride,  257. 

chlorine,  60. 

ozone,  70. 

potassium        permanganate, 
263. 

Ehenic  or  carbolic  acid,  170. 
icement,  collection  of  gases 
by,  25. 

Distillation,  fractional,  146. 
of  coal  tar,  166. 
of  wood,  173. 
the  process  of,  20. 
Distilled  liquors,  183. 

water,  20. 

Doctrine  of  types,  100. 
Drying  gases,  xxv. 
Dualistic  formulae,  100. 


INDEX. 


liii 


Dutch  liquid,  164. 

Dyeing,   methods    of,    198,    260, 

271,  272. 
with  indigo,  200. 
use  of  mordants  in,  260. 
, 

EARTHENWARE,  261. 
Effervescing  liquids,  121,  182, 
Electro-chemical  relations  of  the 

elements,  256,  293. 
Electrolysis  of  water,  16. 
Element,  def.  of,  3. 
Elementary  gases,  molecular  con- 
dition of,  SO.  ... 
Elements  are  bodies  :  incapable  of 

decomposition,  19. 
Empirical  formulae,  98. 
Epsom  salts,  252. 
Equations,  chemical,  calc.  of,  54. 
Equivalent  weights,  286. 
Erbium,  274. 

Essential  oils,  160. ->  ; 

Etching  glass,  67.  '' 
Ethal,  158. 
Ethane,  142. 
Ethene,  165. 
Ether,  148,  149. 

acetic,  150. 
Ethers,  150. 

compound,  150. 
Ethylene,  163. 

chloride,  164. 

series,  165. 

Evaporating-dishes,  xxxi. 
Explosion  of  oxygen  and  'hydro- 
gen, 28. 
Explosions  in  coal-mines,  138. 

FATS,  154. 

artificial,  159. 

saponification  of,  158. 
Fatty  acid  series,  154. 
Fatty  acids  usetl  in  making  can- 
dles, 158. 
Feldspar,  258. 
Fermentation,  143,  161.    :  .  ; 

of  grape-sugar,  144. 
Fermented  liquors,  182. 
Ferric  chloride,  270. 

hydrate,  269.    f    ..! 
29* 


Ferric  hydrate,  used  in  purifying 


oxide,  268. 

corrodes  organic  matter, 
269. 

salts,  270. 

silicate,  271. 

sulphate,  270. 
Ferricyanhydric  acid,  225. 
Ferrocyanhydric  acid,  224. 
Ferrocyanogen,  224. 
Ferrous  and  ferric  salts,  270. 
Ferrous  chloride,  270. 

oxide,  268. 

salts,  270. 

absorb  oxygen,  270. . 
test  for,  272. 

silicate,  271. 

sulphate,  270. 

dyeing  black  with,  270. 

sulphide,  prep,  of,  75. 
Fibrin,  201. 
Filtering,  xxiv. 
Filters,  how  to  fold,  xxiv. 
Fire-damp,  138. 
Flame,  luminosity  of,  125. 

oxidizing,  130. 

put  out  by  good  conductors, 
134. 

reducing,  130. 

structure  of,  128. 
Flames,  all,  gas  flames,  126. 

character  of,  125. 

smoky,  125. 
Flasks,  xxix. 
Flint,  205. 

Flint-glass  contains  lead,  250. 
Fluorhydric  acid,  66. 

action  on  silica,  67. 
prep,  of,  67. 
Fluorine,  66. 

hard  to  get  and  keep,  66. 

occ.  of,  66. 
Fluor-spar,  66. 
Fluosilicic  acid,  206. 
Flux,  used  in  smelting  iron-ores,; 

265. 

Formic  acid,  synthesis  of,  154. 
Formulae,  dualistic,  100. 

empirical  and  rational,  98. 


liv 


INDEX. 


Formulae,  typical,  100. 
Fractional  condensation,  147 
Fractional  distillation,  146. 
Free  gases  exist  as  molecules,  90. 
Friction  matches,  93. 
Fruit-sugar,  180. 
Furnace,  blast,  265. 

reverberatory,  213,  267. 
Furnaces,  xxxiii. 
Fusel  oil,  148. 
Fusible  alloys,  107. 

GALENA,  248,  250. 
Gallium,  274. 
Gallotannic  acid,  195. 
Galvanic  current,  254. 

decomposes  water,  16. 
Galvanized  iron,  254. 
Gas,  illuminating,  139. 
Gas-carbon,  110. 

prop,  of,  111. 
Gas-generator,        self-regulating, 

xxviii. 

Gas-holders,  xix. 
Gas-lamps,  for  heating,  vi. 
Gases,  dissolved  by  water,  21. 

liquefaction  of,  36. 
Gelatin,  202. 
German-silver,  273. 
Glass,  colored,  206. 

comp.  of,  206. 

etching  of,  67. 
Glass  beakers,  xxix. 

cutting  and  cracking,  ii. 


retorts,  xxix. 

tubing,      bending,     drawing 
and  closing,  iii. 

sizes  and  qualities  of,  i. 
Glauber's  salt,  211. 
Glazes,     lead,  —  feldspar,  —  salt, 

261. 

Glucinum,  261. 
Glucosides,  196. 
Glue,  202. 
Gluten,  185. 
Glycerin,  155. 

prep,  of,  156. 

prop,  of,  157. 

uses  of,  157. 


Glycols,  165. 
Gold,  alloys  of,  282. 

coin,  283. 

cyanide,  used  in  gilding,  283 

occ.  of,  281. 

prop,  of,  282. 

salts,  283. 

Gramme,  def.  of,  13. 
Grape-sugar,  179. 
Graphite,  110. 
Graphic  symbols,  289. 
Gray-iron,  266. 
Green  vitriol,  270. 
Group,  the  alkali,  240. 

calcium,  250. 

chlorine,  65. 

nitrogen,  107. 

platinum,  285. 

sesquioxide,  273. 

sulphur,  85. 
Groups,  principles  concerning,  66. 

table  of,  296. 
Gum-arabic,  187. 

benzoin,  167. 

resins,  190. 

spruce,  188. 

tragacanth,  188. 
Gums,  prop,  of,  187. 
Gun-cotton,  187. 
Gun-metal,  275. 
Gunpowder,  226. 
Gutta-percha,  190. 
Gypsum,  245. 

HARD  WATER,  245. 
Hartshorn,  47. 
Homologous  series,  163. 
Horn-silver,  237. 
Hydrocarbons,  variety  of,  137. 
Hydrogen,  derived    from    water, 
15,  16. 

diffusive  power  of,  26. 

explosive  mixture  with  air, 
29. 

with  oxygen,  28. 

extinguishes  combustion^  27.. 

heating  power  of,  27. 

inflammable,  16,  26. 

lightness  of,  25. 

physical  prop,  of,  25. 


INDEX. 


Iv 


Hydrogen,  precautions  in  making, 

23. 

prep,  of,  23. 

prod,  of  combustion  of,  28. 
standard  of   specific  gravity 

for  gases,  25. 

Hydrogen  antimonide,  106. 
arsenide,  102. 

inflammable,  103. 
prep,  of,  102. 
peroxide,  71. 
phosphide,  96. 
comp.  of,  97. 
prep,  of,  96. 
potassium  carbonate,  221. 

sulphate,  225. 
selenide,  86. 
sodium  carbonate,  213. 
sulphide,  76. 

as  reagent,  78. 
sulphide,  comp.  of,  77. 

decomposed  by  metallic 

salts,  78. 

decomposition  of,  77. 
inflammable,  76. 
in  mineral  waters,  77. 
prep,  of,  76. 
soluble  in  water,  76. 
Hypochlorous  acid,  60. 
Hypophosphites,  97. 
Hypophosphorous  acid,  97. 

anhydride,  97. 

Hypotheses  and  theories,  distinc- 
tion between,  4. 

ILLUMINATING-GAS,  139. 

purification  of,  141. 
Indelible  ink,  237. 
India-rubber,  190. 

vulcanized,  191. 
Indigo-blue,  199,  291. 

dyeing  with,  200. 

-white,  199. 
Indigotin,  199. 
Indium,  261. 
Ink,  195. 

indelible,  237. 
Inulin,  184. 
lodates,  64. 
lodic  acid,  64. 


Iodine,  occ.  and  prop,  of,  62. 

occurs  crystallized,  63. 

reaction  with  starch,  63. 

specific  gravity  of  vapor,  63. 

testing  for,  63. 

uses  of,  64. 

lodohydric  acid,  prop,  of,  64. 
lodo-starch  paper,  63. 
Iridium,  285. 
Iron,  cast-,  264. 

impurities  of,  266. 
varieties  of,  266. 

extraction  of,  264. 

galvanized,  254. 

mordant,  271. 

occ.  of,  264. 

ores,  264. 

puddling  of,  266. 

pyrites,  273. 

sulphide,  prep,  of,  75. 

wrought,  264. 
Iron  cyanides,  272. 

hydrates,  268,  269. 

oxides,  268,  269. 

sulphates,  270. 

sulphides,  272,  273. 
Iron  retort,  xxxiii. 
Iron  stand  for  supporting  vessels, 

xiv. 

Isinglass,  202. 

Isomeric,  term  defined,  154. 
Isomerism,  173. 
Isomorphism,  231. 

KAOLIN,  261. 

Kindling- temperature,  132. 

Kreasote,  173. 

LACTOSE,  181. 
Lakes,  260. 
Lampblack,  112. 

manufacture  of,  112,  114. 
Lamp-flames  are  gas-flames,  126. 
Lamps  for  laboratory  use,  vi. 
Lanthanum,  274. 
Lard,  154. 
Laughing-gas,  33. 
Laurie  acid,  159. 
Law  of  Ampere,  89. 
Laws,  chemical,  4. 


Ivi 


INDEX. 


Lead,  action  of  acids  on,  249. 

action  of  water  on,  249. 

classed  with  the  calcium 
group,  250. 

crystallization  of,  248. 

metallic,  prop,  of,  248. 

red-,  250. 

testing  for,  250. 

tree,  255. 

use  of,  for  water-pipes  and 
cisterns,  249. 

white-,  250. 
Lead  acetate,  250. 

carbonate,  249,  250. 

hydrate,  249. 

peroxide,  250. 

protoxide,  249,  250. 

silicate,  250. 

suboxide,  249. 

sulphide,  248,  250. 
Leather,  195.     • 
Leblanc's  process,  212. 
Legumin,  202. 
Levulose,  180. 
Liebig's  condenser,  21,  146. 
Light,  action  of,  on  silver  salts, 
238. 

artificial,  125. 
Light  oil  of  tar,  166. 
Lime,  heat  evolved    in  slaking, 
243. 

milk  or  cream  of,  243. 

slaked,  absorbs  carbonic  acid 
and  hydrogen  sulphide, 
244. 

the  cheapest  base,  244. 

uses  of,  244. 
Lime,  caustic,  244. 

-water,  243. 
Limestone,  241. 
Lines  of  cleavage^  74. 
Liquors,  distilled,  183. 

fermented,  182. 
Litharge,  249, 
Lithium-flame,  232. 
Lithium,  occ.  of,  231. 

resembles  sodium  and  potas- 
sium, 231. 
Litmus-paper,  40. 

I,  dyeing  with,  198. 


Luminosity  of  flames,  "125. 
Luminous  flames,  form  of,  128. 
Lunar  caustic,  237. 

MADDER,  197. 
Magenta,  170..    -      •    .   •, 
Magnesia,  251. 

alba,  252. 

crucibles,  252. 
Magnesium  light,  251. 

oce.  and  prop,  of,  251. 

salts,  from  mother-liquor  of 

salt-works,  210. 
Magnesium  carbonate,  252. 

chloride,  252. 

citrate,  194. 

oxide,  252. 

sulphate,  252. 
Malic  acid,  193. 
Manganates,  263. 
Manganese,  occ.  of,  262. 
Manganese,  binoxide,  262. 

chloride,  263- 
Manganic  acid,  263. 
Manufacture  of  illuminating  gas, 
139. 

of  soap,  155. 

of  sugar,  1 76. 
Maple-sugar,  178. 
Marble,  241.  - 

Marsh-gas,   137,  see   Methyl  hy-r 
dride. 

series,  142. 
Matches,  93,  95, 
Meconic  acid,  196. 
Mercaptans,  150. 
Mercuric  -chloride,  279. 

an  antiseptic,  279. 
Mercurous  chloride,  279. 
Mercury,  alloys  of,  279. 

detection  of,  279. 

extraction  of,  277. 

pneumatic  trough,  xvi. 

prop,  of,  278. 

symbol  of  atom  and  molecula 
the  same,  91,  278. 

unit-volume   weight  half  its 
atomic  weight,  91,  278. 

uses  of,  277. 
Mercury  oxide,  red,  278. 


INDEX. 


Ivu 


Mercury  suhoxide,  278. 

:  sulphide,  278. 

Metal,  meaning  of  the  term,  235. 
Metallic  elements,  235. 
Metaphosphoric  acid,  98. 
Meteoric  iron,  264. 
Methyl  alcohol,  148. 

formate,  154.    . 

hydride,  oce.  of,  137. 
Methane,  142. 
Methylated  spirit,  148. 
Metre,  def.  of,  xxxvi. 
Metrical  system  of  weights  and 

measures,  xxxvi. 
Milk,  202. 
Milk-sugar,  181. 

Molecular  condition  of  elemen- 
tary gases,  89. 
Molecule,  def.  of,  18. 
Molybdenum,  295. 
Mordants,  199,  260. 
Morphia,  196. 
Mortar,  244. 
Mortars,  xxxiv. 
Mouth-blowpipe,  use  of,  129. 
Mouth-blowpipes,  xi. 
Mucilage,  vegetable,  188. 
Multiple  proportions,  law  of,  37. 
Muriatic  acid,  49. 

manufacture  of,  51. 

NAPHTHALIN,  172. 
Nascent  state,  54. 
Natural  fats  and  oils,  154. 
Negative  elements,  256. 
pole  of  battery,  256. 
Neutralization,  42. 
Nickel,  273. 
Nicotine,  197. 
Nitrates,  43. 

natural  formation  of,  225. 
Nitre,  225. 
Nitric  acid,  comp.  of,  36. 

prep,  of,  39. 

prop,  of,  40. 

sources  of,  39. 
Nitric  anhydride,  36. 
Nitric  oxide,  comp.  of,  34. 

prep,  of,  33. 
Nitro-benzol,  production  of,  167. 


Nitro-benzol,  prop,  of,  168, 

use  of,  168. 
Nitro-cellulose,  187. 
Nitro-glycerin,  157. 

comp.  of,  157. 

prep,  and  prop,  of,  157. 
Nitrogen,  a  constituent  of  air,  8. 

and  hydrogen,  44. 

binoxide,  see  Nitric  oxide. 

chloride,  64. 

dilutes   the   oxygen    in    air, 
13. 

group,  107. 

iodide,  64. 

obtained  from  air,  12. 

oxides  of,  37. 

peroxide,  35. 

physical  prop,  of,  12. 

prep,  of,  12. 

by  phosphorus,  12. 

protoxide,  comp.  of,  32. 
prep,  of,  31. 
prop,  of,  31. 

widely  diffused,  13. 
Nitrous  acid,  37. 
Nitrous  anhydride,  36. 
Nitrous  oxicle,  see  Nitrogen  prot- 
oxide. 

Nomenclature,  287. 
Non-metallic  elements,  235. 

OCHRE,  red,  268. 
yellow,  269. 

Oil  of  bitter  almonds,  174. 
of  cloves,  160. 
of  turpentine,  comp.  of,  162. 
prop,  of,  161. 
use  as  solvent,  161. 
olive,  154. 

of  vitriol,  manufacture  of,  83. 
Oils,  154. 

drying,  159. 
essential,  160. 
fixed,  159. 
vegetable,  159. 
Olefiant  gas,  163. 

prep,  of,  164. 

present  in  illuminating 

gas,  141. 
series,  165. 


Iviii 


INDEX. 


Oleic  acid,  155. 

Olein,  154. 

Opium,  196. 

Order-list  of  chemicals,  xlii. 

of  utensils,  xliv. 
Organic  chemistry  denned,  135. 
Organic  coloring  matters,  197. 

substances,  decay  of,  203. 
Orpiment,  105. 
Osmium,  285. 
Ossein,  202. 
Oxalates,  192. 
Oxalic  acid,  192. 

comp.  of,  193. 
prep,  of,  192. 
Oxidation,  11,  290. 
Oxidizing  agents  denned,  81,  290. 

flame,  130. 

Oxygen,   abundance  and   impor- 
tance of,  11. 

burning    charcoal,    etc.     in, 
10. 

burns  in  hydrogen,  30. 

constituent  of  air,  8. 

explosive  mixture  with  hy- 
drogen, 28. 

physical  properties  of,  9,  10. 

precautions  in  making,  9. 

prep,  of,  9,  247. 

supports  combustion,  10. 
Oxy-hydrogen  blowpipe,  27,  129. 
Ozone,  68. 

atmospheric,  70. 

disinfecting  agent,  70. 

prep,  by  electricity,  68. 

prep,  by  phosphorus,  69. 

prop,  of,  69. 

resembles  chlorine,  68,  69. 

tests  for,  69. 

PALLADIUM,  285. 
Palm-sugar,  178. 
Palmitic  acid,  155. 
Palmitin,  154. 
Paraffin,  158,  174. 
Parchment-paper,  186. 
Parchment,  vegetable,  186. 
Pearlash,  220. 
Pectic  acid,  189. 
Pectin,  188. 


Pectose,  188. 
Pectosic  acid,  189. 
Permanganates,  263. 
Petrefactions,  calcareous,  242. 
Petroleum,  comp.  of,  142. 

occ.  of,  142. 
Pewter,  280. 
Phenates,  171. 

antiseptic  prop,  of,  171. 

used  as  disinfectants,  171. 
Phenic  acid,  170. 
Phenol,  171. 
Phenyl  alcohol,  171. 

series,  166. 
Phenylamine,  159. 
Phosphates,  98. 
Phosphides,  96. 
Phosphites,  97. 
Phosphorescence,  94. 
Phosphoric  acid,  98. 

meta-,  98. 

pyro-,  98. 

tri-basic-,  98. 

Phosphoric  anhydride,  affinity  of 
for  water,  98. 
prep,  of,  98. 
Phosphorus,  allotropism  of,  94. 

burnt  under  water,  227. 

common,  92. 

comparison  of  red  with  com- 
mon, 95. 

compounds  with    hydrogen, 
96. 

inflammability  of,  93. 

manufacture  of,  246. 

occ.  of,  92. 

oxides  of,  97. 

red,  94. 

converted  into  common, 

95. 
on  safety-matches,  95. 

shines  in  the  dark,  94. 

solutions  of,  94. 

unit-volume  weight  of,  97. 
Phosphuretted    hydrogen,    comp. 
of,  97. 

prep,  of,  96. 
Photography,  238. 
Physical  changes,  2. 
Physiological  chemistry,  200. 


INDEX. 


lix 


Picrates,  172. 
Picric  acid,  prep,  of,  172. 
prop,  of,  171. 
used  in  dyeing,  198. 
Pincers,  xxxiv. 
Pipettes,  xxxi. 
Plaster  of  Paris,  245. 
Plaster-casts,  245. 
Plastering,  comp.  of,  244. 
Platinum,  alloys  of,  284. 

black,  284. 

foil  and  wire,  xxiii. 

group,  285. 

induces  combination,  284. 

melting  of,  283. 

metals,  285. 

occ.  and  prop,  of,  283. 

sponge,  prep,  of,  285. 

uses  of,  284. 

vessels,  precautions  in  using, 

284. 

Platinum  chloride,  284. 
Plumbago,  110. 
Pneumatic  troughs,  construction 

and  use  ol,  xv. 
Polarized  light,  action   on   sugar, 

179. 
Porcelain,  261. 

dishes,  xxxi. 
Positive  elements,  256. 

pole  of  battery,  256. 
Potash,   obtained  from  ashes  of 

plants,  220. 
Potassium  bicarbonate,  221. 

bromide,  223. 

carbonate,  220. 

chlorate,  227. 

prep,  of  oxygen  from,  9. 

chloride,  223. 

cyanide,  223. 

ferricyanide,  224. 

ferrocyanide,  224. 

formate,  153. 

hydrate,  221. 

prep,  of,  221. 
uses  of,  221. 

iodide,  223. 

manganate,  263. 

metallic,  222. 

nitrate,  225. 


Potassium,   nitrate,   an  oxidizing 

agent,  226. 
occurs  iii  nature,  225. 

permanganate,  263. 

a  disinfectant,  263. 

picrate,  172. 

sulphate,  225. 

tartrate,  228. 
Preservative  agents,  204. 
Product-volume  defined,  88. 
Proto,H(n),  &c.,  34. 
Prussian  blue,  272. 
Prussic  acid,  136. 
Puddling  iron,  process  of,  266. 
Pulverizing,  xxxv. 
Pyrites,  273. 
Pyroligneous  acid,  153. 
Pyrophosphoric  acid,  98. 
Pyroxylin,  187. 

QUANTIVALENCE,  53,  288. 

of  radicals,  100.    . 
Quartz,  205. 
Quercitannic  acid,  195. 
Quicklime,  manufacture  of,  243. 
Quicksilver,  277. 
Quinine,  196. 

RADICAL,  acetyl,  152. 

allyl,  162. 

ammonium,  46. 

benzoyl,  174. 

cyanogen,  136. 

ethyl,  143. 

ferricyanogen,  225. 

ferrocyanogen,  224. 

glyceryl,  155. 

methyl,  137. 

phenyl,  167. 
Radicals  of  fatty  acids,  152. 

of  marsh-gas  series,  143. 

compound,  101. 
Rational  formulae,  98. 
value  of,  154. 
Reaction,  acid  and  alkaline,  40. 

def.  of,  24. 
Realgar,  105. 
Red  lead,  250. 
Reducing  agent  denned,  81«  290. 

flame,  130. 


INDEX. 


Reduction  of  metals  by  carbonic 
oxide,  124. 

charcoal,  115,  119. 
Relation  of  chemical  energy  to 

atomic  weight,  66. 
Replacing  power,  53. 
Resinic  acid,  190. 
Resins,  189. 

fossil,  191. 

gum,  190. 
Retort,  iron,  xxxiv. 
Retorts,  glass,  xxix. 

in  manufacture  of  gas,  139. 
Reverberatory  furnace,  213,  266. 
Rhodium,  285. 
Rochelle-powders,  194,  214. 

salt,  194,  214. 
Rock-candy,  179. 

crystal,  205. 
Rosin,  161,  189,  190. 
Rouge,  268. 
Rubidium,  233. 
Ruby,  258. 

Rust,  of  tin,  iron,  mercury,  &c., 
contains      something    de- 
rived from  the  air,  6,  11. 
Rusts  are  oxides,  11. 
Ruthenium,  285. 

SAFETY-lamps,  134. 

-matches,  95. 
Sago,  184.  _ 
Sal-ammoniac,  229. 
Sal  volatile,  230. 
Saleratus,  221. 

Saline  taste  and  substance,  209. 
Salt,  def.  of  term,  41,  42. 
Salts   of     radicals  of  marsh-gas 

series,  150. 

Salt  (common),   manufacture  of, 
209. 

glaze,  211. 

solubility  of,  210. 

sources  of,  209. 

uses  of,  210. 

Saltpetre,  see  Potassium  nitrate. 
Sand-bath,  xiv. 
Saponifi cation,  def.  of,  158. 
Sapphire,  258. 
Saturated  solutions,  22. 


Selenic  acid,  86. 
Selenium,  85. 
Series,  acetylene,  175. 

benzyl,  175. 

ethylene,  165. 

fatty  acid,  152. 

homologous,  163. 

marsh -gas,  142. 

olefiant  gas,  165. 

phenyl,  166. 
Sesquioxide,  def.  of  term,  269. 

group,  273. 

Shot,  arsenic  added  to,  102. 
Silica,  see  Silicic  anhydride. 
Silicates,  205. 

alkaline,  soluble,  206. 

in  glass,  206. 
Silicic  acid,  205. 
Silicic  anhydride,  205. 

occ.  of,  205. 
Silicic  ethers,  207. 
Silicon,  abundance  of,  204. 

allotropic  conditions  of,  207. 

in  organic  compounds,  207. 
Silicon  fluoride,  206. 
Silver    classed    with    the    alkali 
metals,  240. 

coin,  236. 

horn,  237. 

occ.  of,  234. 

prop,  of  metal,  235. 

separation  from  lead  by  crys- 
tallization, 248. 
Silver  bromide,  237. 

chloride,  237. 

cyanide,  238. 

hydrate,  238. 

iodide,  237. 

nitrate,  236. 

oxides,  238. 

sulphate,  238. 

sulphide,  238. 
Silvering  of  mirrors,  279. 
Soap,  cleansing  action  of,  216. 

hard  and  soft,  156. 

manufacture  of,  155. 
Soaps,  insoluble,  156. 
Soda-ash,  manufacture  of,  212. 

bicarbonate  of,  214. 

-crystals,  213. 


INDEX. 


Soda,  grocers',  214. 

-water,  122. 
Sodium  flame,  232. 

occ.  of,  209. 

prop,  of,  214. 
Sodium  biborate,  217. 

bicarbonate,  213. 

carbonate,  212. 

chloride,  209. 

hydrate,  215. 

hydrogen  carbonate,  213. 
sulphate,  211. 

hyposulphite,  219. 

nitrate,  218. 

phosphates,  218. 

silicates,  219. 

sulphate,  211. 

sulphides,  218. 
Solder,  280. 

Soldering,  use  of  chloride  of  zinc 
in,  257. 

sal-ammoniac  in,  230. 
Soluble  glass,  205. 
Solution  denned,  22. 

of  gases  in  water,  21. 

saturated,  22. 
Spatulse,  xxxv. 
Specific  gravity,  def.  of,  14. 
of  gases,  25. 

relation  to  combin- 
ing weight,  88. 
Spectrum  analysis,  232. 

delicacy  of,  233. 
Spermaceti,  comp.  of,  158. 
Spongy  platinum,  285. 
Spontaneous  combustion,  160. 

of  coal,  273. 
Stalactites,  242. 
Stalagmites,  242. 
Stannates,  281. 
Stannic  acid,  281. 
Starch,  occ.  of,  183. 

-paste,  63. 

prop,  of,  184. 

-sugar,  179. 
Steam,  dry,  17. 

physical  prop,  of,  14. 

volumetric  comp.  of,  18. 
Stearic  acid,  155. 
Stearin,  154. 

30 


Steel,  267. 

Bessemer,  268. 
Stereotype-metal,  105. 
Stove-polish,  110. 
Straw-rings,  xxxii. 
Strontianite,  248. 
Strontium,  247. 

compounds,  247. 

flame,  248. 

Structure  of  flames,  128. 
Strychnine,  196. 
Substitution  compounds,  173. 
Succinic  acid,  191. 
Sucrose,  176. 

Sugar,  action  of  polarized    light 
on,  179. 

barley,  179. 

beet-,  178. 

brown,  177. 

cane-,  176. 

manufacture  of,  176. 
prop,  of,  179. 
refining  of,  177. 

fermentation  of,  144,  181. 

fruit-,  180. 

grape-,  179. 

maple-,  178. 

milk-,  181. 

of  lead,  250. 

palm-,  178. 

starch-,  179. 

varieties  of,  176. 
Sulphates,  85. 
Sulphides,  75. 
Sulphindigotic  acid,  199. 
Sulphur,  crystallization  of,  73. 

dimorphous,  75. 

extraction  of,  72. 

group,  86. 

kindling  material,  93. 

melting  of,  72. 

metals  burn  in,  75. 

milk  of,  219. 

occ.  of,  71. 

purification  of,  72.  > 

salts  compared  with  oxygen 
salts,  86. 

soft,  73. 

solution  of,  74. 
Sulphuretted  hydrogen,  76. 


Ixii 


INDEX. 


Sulphuric  acid,  81. 

absorbs  water,  84. 

action  on  metals,  79. 
organic  matter,  84. 

bibasic,  85. 

concentration  of,  83. 

fuming,  85. 

how  to  mix  with  water, 
84. 

importance  of,  81. 

manufacture  of,  82. 
Sulphuric  anhydride,  81. 
Sulphurous  acid,  78. 

bleaches,  80. 

comp.  of,  80. 

Sulphurous  anhydride,  comp.  of, 
80. 

liquid,  79. 

oxidation  of,  81. 

prep,  of,  78,  79. 

prop,  of,  79. 

stops  combustion,  79. 
Superphosphate  of  lime,  246. 
Supporters  of  combustion,  29. 
Symbols,  chemical,  24,  289,  291. 
Synthesis,  def.  of,  3. 
Systems  of  crystallization,  74. 

TABLE  of  atomic  weights  and 
symbols  of  the  elements, 
286. 

for  conversion  of  centigrade 
into  Fahrenheit  degrees, 
xli. 

for  conversion  of  French  into 
English  weights  and  meas- 
ures, xl. 
of     elements     arranged    in 

groups,  290. 
Tables  of  metrical   weights   and 

measures,  xxxvii. 
Tannic  acid,  194. 

test  for,  195. 
Tannin,  194. 
Tantalum,  295. 
Tapioca,  184. 
Tartar,  193. 
Tartar-emetic,  194. 
Tartaric  acid,  prep,  of,  193. 
uses  of,  194. 


Tartrates,  194. 

Tellurium,  86. 

Temperature,  kindling-,  132. 

Terminations  ous  and  tc,  34. 

Test-glasses,  xxxi. 

Test-tubes,  xxx. 

Thallium,  234. 

Theine,  197. 

Theobromine,  197. 

Thermometers,  xxxv. 

Thermometer-scales       compared, 

xli. 

Thorium,  274. 
Tin,  crystallization  of,  280. 

extraction  of,  280. 

prop,  of,  281. 
Tin  bisulphide,  281. 

oxides,  281. 
Tin-stone,  280. 
Tinned  iron,  281. 
Titanium,  295. 
Toluol,  167. 
Toluidine,  170. 
Tongs,  xxxiv. 
Touch-paper,  131. 
Travertine,  242. 
Trinitrophenic      acid,  see   Picric 

acid. 
Tubing,  caoutchouc,  xii. 

glass,  sizes  and  qualities  of,  i 
Type-metal,  105. 
Types   of    chemical    compounds, 

100. 
Typical  formulae,  100. 

examples  of,  101. 

hydrogen  compounds,  101. 

UNION  of  hydrogen  and  oxygen, 

29. 

Unit- volume  weights,  292. 
Univalent,  the  term  denned,  53. 
Uranium,  274. 

VACUUM-PAN,  177. 

princ.  of,  illustrated,  178. 
Vanadium,  295. 
Vapor  density,  90. 

value  of  determining,  165. 
Varnishes,  190. 
Vegetable  acids,  191. 


INDEX. 


Ixiii 


Vegetable  albumin,  201. 

alkaloids,  196. 

fibrin,  201. 

mucilage,  188. 

oils,  159. 

parchment,  186. 

Vegetables,    proximate    constitu- 
ents of,  176. 
Verdigris,  277. 
Vermilion,  278. 
Vinegar,  151. 
Vitriol,  blue,  277. 

green,  270. 

white,  257. 

Volume,  combination  by,  87. 
Volumetric  composition,  92,  291. 

WATER,  analyzed  by  iron,  15. 
by  sodium,  15, 

densest  at  4°,  14. 

dissolves  air,  21. 

distillation  of,  20. 

electrolysis  of,  16. 

hardness  of,  245. 

occ.  of,  13. 

produced  by  burning  hydro- 
gen, 28. 

prop,  of,  14. 

purity  of  natural,  19. 

removal  of  gases  from,  21. 

the  common  solvent,  22. 

standard  of  specific  gravity, 
14. 

symbol  of,  18. 

synthesis  of,  17. 

volumetric  comp.  of,  18. 
Water-bath,  xxvii. 
Waterglass,  205. 


Waterglass,  uses  of,  206. 
Wedgewood  mortars,  xxxiv. 
Weight,  molecular,  24  a,  44. 
Weights,  atomic,  19. 

metrical,  xxxvi. 

comparison  of,  xl. 
White  indigo,  199. 

iron,  266. 

lead,  250. 

vitriol,  257. 
Wines,  182. 

Wire-gauze,  use  of,  xiv. 
Wood,  distillation  of,  173. 

preservation  of,  171,  257. 
Wood-spirit,  148. 
Woody  fibre,  186. 
Woulffe-bottles,  48. 
Wrought-iron,  266. 

YEAST,  143. 
Yeast -powders,  214. 
Yellow  metal,  275. 
Yttrium,  274. 

ZINC,  action  of  acids  on,  254. 
air  on,  253. 

alloys  of,  254. 

dust,  253. 

granulated,  253. 

ores  of,  252. 

prop,  of,  252. 

replaces  lead,  255. 

white,  257. 
Zinc  chloride,  24,  257. 

oxide,  257. 

sulphate,  257. 

sulphide,  252. 
Zirconium,  274. 


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